The ancient Greeks, the most influential culture of all time, encapsulated this by making lists of the monumental constructions they found most awesome, labeling them the Seven Wonders. Only one of these wonders of the ancient world stands today, the Great (Cheops) Pyramid. In a sense all the Seven Wonders were messages intended to provoke in us remembrance mingled with awe, and as such six have failed.

A tour of the sites of the Seven Wonders is instructive. No ancient could have seen them all, since they did not all exist simultaneously. There were several ancient lists of the Seven Wonders, each heavily favoring the Greeks, who wrote them. The Palace of Cyrus, king of rival Persia, was discreetly ignored. The Temple of Solomon in Jerusalem might have made the list, but was a shrine to a barbarian god, after all.

The fabled Hanging Gardens of Babylon, of which we have not a single authentic image, seems to have been abandoned and scavenged within centuries. No trace remains of them, and we have only a vague idea (from texts) of how the hidden plumbing kept them lushly green.

In present day Turkey stood the Temple of Artemis, built at Ephesus in 550 B.C. when the region was in the Greek cultural orbit. Writing in 60 A.D., Pliny the Elder called it "the most wonderful monument of Grecian magnificence." Made of white marble, it was 425 feet long, 225 feet wide and with its more than a hundred 60-foot stone columns supported a massive roof. Its ornamental sculptures and paintings were said to be of extraordinary beauty. Today a lone bare column sticks up from a muddy field, so unremarkable and unmarked that visitors often drive right past the site. Burned down in the fourth century B.C., the Temple was rebuilt in the third and then sacked and destroyed by the Goths in A.D. 362.

The most renowned sculptor of antiquity, Phidias, created two of the Wonders: the Colossus of Rhodes and the Olympian Statue of Zeus, around 435 B.C.. The bronze Colossus stood as tall as the Statue of Liberty and was even more massive, yet fell in an earthquake only fifty-six years after it was erected. They were both vandalized by invaders within centuries. No authenticated parts survive.

The Mediterranean was a pleasant, warm region for developing human culture, but its crust was unstable. Several of the Wonders were damaged or destroyed by earthquakes. The Lighthouse of Alexandria, c. 280 B.C., stood a striking 350 ft. (105 m) high, dominating the harbor, but fell in an earthquake in the 13th century. Of particular poignancy was the Mausoleum of Halicarnassus (c. 352 B.C.) on what is now the Turkish coast. The widow of the tyrant Mausolus finished this tomb, spending a fortune embellishing the tower with the finest statuary and encrustations of the Mediterranean basin. Mausolus apparently began his own tomb construction, echoing the pharaohs, who had work start upon their ascension to the throne; ruler cults demand constant attention.

As described by Pliny in the first century A.D, this magnificent tomb struck his era as comparable in impact with the pyramids. Tapered using three step-backs, the tomb rose some fifty meters to an artistic climax: 36 columns in colonnade supporting a roof whose 24 steps carry a colossal four-horse chariot of marble. With elaborate friezes carved in relief, one of battle scenes with centaurs, another with Amazons, and sculptures ranging from natural to colossal in size, its point lay below, where a staircase nine meters wide led down to the tomb chamber.

Mausolus was cremated before burial on a huge public pyre. His tomb was crammed with riches (all stolen later), stocked with slaughtered calves, cows, sheep and hens, and cleverly drained by ducts along its walls. A solid pile of stone blocks filled the staircase, was covered with earth, and finally a plug rock barred entrance. Robbers plundered it by digging a tunnel into the rock beneath the foundations.

Mausolus ruled as a Persian satrap, filling his treasury by taxing even those who wore their hair long. He was shrewd, unscrupulous, and much feared and hated by his subjects, who several times attempted assassination.

The tomb gained its grandeur not from scale but from ornamentation, and this may well have proved its undoing. Shaken by a distant quake, statuary slid down the roof and crashed into other figures, such as the large stone lions who stood guard in front. There is archeological evidence that this occurred. Shifts of the rock made the marble facing crack and peel away. Such degradations apparently disfigured the building long before it fell.

Finally, the structure proved top-heavy and vulnerable, so that a final quake in A.D. 1304 brought it all down. The Crusaders investigated the ruin, dug and found the burial chamber, but were forced by the raids of Arab infiltrators to abandon it at nightfall. When they returned the next day the tomb had been looted, and much of the testament to the greatness of the tyrant was gone. It was never recovered. Later these same knights used the ruins as a quarry to erect a castle that still stands today.

When I visited the site, littered with drums of stone that once were part of the grand columns, there remained only an air of shattered grandeur. Like several of the Wonders, this monument could have been repaired after quake damage, but the urge to do so had ebbed away. Mausolus's primary legacy is a word, mausoleum.

Not even all of the pyramids of Egypt survived. The vast mud-brick pyramids sustained serious quake damage. The large pyramid at Medium is today a three-step pygmy compared with the original, whose limestone outer casings form a jumbled skirt around it.

The Pharaohs apparently built the pyramids to solidify their hold on the world's first and greatest Thantocracy. Organizing society around death demanded convincing demonstrations of mastery by those who said they held open the portal to eternity. Shaped to call forth comparison with mountains, the pyramids were the largest objects visible within the narrow world of the river-centered nation. They made Pharaonic power obvious to all and promised a firm solution to the most basic of all human problems, the dilemma of death. Construction provided worthy labor to the peasant masses during the Nile's flood season, when idle hands might make trouble for the state.

The pyramid pinnacles carried capstones sheathed in gold; the only surviving specimen is covered in religious symbols. Greek travelers beheld the Great Cheops Pyramid clad in fine white limestone, a dazzling sight from many miles away with its gold peak. The limestone was stripped away millennia ago to build Cairo. We see only the core, rugged and massive and still awe-inspiring. Indeed, the pyramids were man-made mountains, proclaiming that the state could echo nature's feats.

Critics have berated the pharaohs for spending great wealth on such useless monuments. Of course, the pharaohs did not see them as useless, but rather as a sure way to gain a pleasant afterlife. Further, Egyptian engineers learned much about quarrying, shaping and maneuvering large blocks, learning that passed into humanity's general knowledge.

The Egyptians set a pattern seen often in antiquity. Ancient palaces were mostly built of mud brick, and eroded quickly. Since this passing vale of tears was far less important than an eternal afterlife, this was proper, just as building tombs and temples of stone fitted their enduring importance.

A funereal air surrounds lasting monuments down into our time. Tombs on aging European estates have outlasted several great houses nearby. Of course, even mass does not guarantee that your message will remain in context. The largest obelisk of ancient Egypt was 105 feet long and now resides in Rome, its intention ignored.

We cultural descendants of the Greeks have canonized the Seven Wonders, but equally powerful works appeared in antiquity, far from the Mediterranean Basin. The Great Wall of China, the only ancient construction so large it is visible from space, was unknown to classical Western civilizations. The huge dam at Ma'rib in Arabia and the Buddhist stupas of Ceylon surely would have made the list if the Greeks had voyaged farther. The Nazca Plain lines and Easter Island heads, while more recent, might have made the list.

Perhaps the best known architecture of antiquity is the Acropolis of Athens, with its Parthenon and other buildings. It was not on most of the several Seven Wonders lists. Dating from the fifth century B.C., it was a trans-cultural religious site for Greeks, Romans, Christians and Muslims. Some metal statues were "recycled" in antiquity. Removal of some pieces to indoor museums (notably the Elgin Marbles to London) prolonged the durability of some statues, friezes and columns and spread the Acropolis's renown as a cultural artifact worth preserving. Only modern acid rain has damaged it appreciably, arguing against returning the scattered pieces to the original, outdoor structures. The crowning glory of the Acropolis, the Parthenon, has become a pervasive standard for architectural beauty.

Strikingly, no libraries survived antiquity intact, though some were quite grand. (Pieces of some were salvaged and passed on.) A Christian mob burned the greatest trove of ancient writings, the Library of Alexandria, taking from us hundreds of thousands of papyrus and vellum scrolls. Writing on organic sheets is vulnerable to fire, whether from fanatics or accident. Acid-free paper withers in a few centuries.

Stone lasts. It is still the wisest deep time investment.

The oldest reliably dated structure in North America is a 5,400-year-old earthen mound at Watson Brake, Louisiana, fully 2,000 years older than the much better known, classic mound-builder sites of other river valleys. Thousands of artificial mounds dot the U.S.A.'s east and midwest, shaped like serpents, giant cones or square platforms. Though some were used as ceremonial centers and slaughterhouses, their purpose remains mostly mysterious.

The civilization that built them had no writing or pictorial displays, yet sent the simple message of impressive large structures across millennia. Their prolonged earnestness is clear, since the Watson Brake site apparently took 400 years to finish, yet trade and agriculture do not seem to be the primary motivations behind the builders. Asked for their purpose, an archeologist remarked, "I know it sounds awfully Zen-like, but maybe the answer is that building them was the purpose."

No one ever lived in this mound area. Perhaps it had a special aim beyond the everyday. Such long-lived sites transmit a blunt signal of existence, no more. Perhaps this makes them all the more compelling, for the silences of such sites seems to have a significance of its own.

This brief tour of antiquity shows that the high cultures of many civilizations sought to propagate or commemorate itself in permanent ways. That they often failed only underlines how difficult the task is. We know of many failures, but can only contemplate the probably larger number we do not know.

Doubtless many went to their graves believing some sliver of their identity would ring down through the corridors of time. Few did.

What will last from our own time?

In 1995 the American Society of Civil Engineers produced a list of the Seven Wonders of the United States. Two were holdovers from a similar list they compiled in 1955, the Hoover Dam and the Panama Canal. Dropped from that earlier list were the San Francisco Bay Bridge, the Empire State Building, the Grand Coulee Dam, the Colorado River Aqueduct and the Chicago sewage disposal system (surely a wonder suited particularly to engineers' discernment).

All these still proudly stand, but apparently the engineers now find them less wondrous. In merely forty years they have yielded to the Golden Gate Bridge, Manhattan's World Trade Center, the Kennedy Space Center, the Trans Alaska Pipeline and the overall Interstate Highway System. While the first two provoke awe, the others do not possess the singular impact I associate with wonder. This suggests that our sense of the awesome is quite personal. Deep time messages must speak to feelings of wonder that persist across both time and culture.

Arthur C. Clarke mentioned to me his choice of the Seven Wonders of the Modern World: the Saturn V rocket, the microchip, the rock fortress of Sigirya (a Sri Lankan temple invoked in his novel, The Fountains of Paradise), the Mandelbrot Set (a mathematical figure which set off the vogue for fractals), Bach's Toccata and Fugue in D Minor, the giant squid, and SS-433 (an astronomical object which projects twin jets of matter in opposite directions from its core, moving at a precise fraction of the speed of light).

This is really a mixed list of accomplishments and objects, the last two natural. When I quibbled about this, he leaned back with his British grace and said, "I mean that discovering them is a wonder."

Alas, Clarke's list betrays a distortion familiar in ancient inscriptions: up close, events loom large.

Minor battles seem to rival Gettysburg. Stature dwindles along with immediacy. His addition of the microchip suggests a difference between our present technological triumphs and those of the past. We can be inspired by quite tiny things which pack enormous information densities into their compass. But will such passing marvels provoke wonder in future minds?

This question suggests that we study the primary deep time communication methods used in the past, hoping they will work into the future.

Undertakings to convey the best of current culture seem to have had the best chance of surviving, for their beauty could protect them for at least a time from random vandalism. These attempts I shall call High Church: communicating the culture of the upper crust, usually solely of the politically powerful class. Often the High Church strategy conveys more than it intends; for example, we read into Egyptian hieroglyphics class and economic issues that the artists assumed natural and unremarkable, hence invisible.

A parallel note sounds down through the millennia: Kilroy Was Here. This rather mysterious graffito emerged in the twentieth century, the point being perhaps that nobody knows who Kilroy was, but he (she?) thought himself important enough to leave his mark. Indeed, who among us does not?

Kilroy is an old phenomenon. The last of the major step pyramids of Egypt is at Saqqara. It set the trend in design, today appearing as a high rectangular tower with a base engulfed in sand. A thousand years after it rose, someone scribbled on a wall of its mortuary temple that he had come "to see the beautiful temple of King Snefru." though we are not sure exactly who was buried there. The sight was glorious: "May heaven rain with fresh myrrh, may it drip with incense upon the roof of the temple . . . " Other graffiti festoon the pyramid. Greek mercenaries of 700 B.C. left their names on many Egyptian monuments.

Indeed, even the famous are not immune; Lord Byron's name is carved into the Temple of Poseidon at Cape Sounion. In the early 1800s a British traveler in Egypt incongruously named Giovanni Belzoni flamboyantly cut his appellation into many monuments, making himself well known to modern visitors by sheer irritating persistence. Though now disparaged by Egyptologists, he accomplished the aim of Kilroyism: sending at least his name across the abyss of years.

This simple, universal impulse gives us the most common type of deep time message. In nooks and crannies of once-great buildings, one finds the cut or carved or scrawled evidence of a desire to not go unheralded into oblivion: Kilroy lives.

The Kilroy impulse is both predictable and deplorable.

When I was working on the marker to fly with the Cassini Saturn probe, we learned that a Jet Propulsion Lab (JPL) group had begun to create their own marker. Previous missions all the way back to the Mars Viking lander, and perhaps even earlier, had carried the names of principal engineers, etched onto metal strips. Why not expand this idea and include the public?

With little time to spare, this Kilroy Was Here gesture could attract attention, public involvement, more hits at the Cassini web site. The Planetary Society joined in. Anyone who wanted their name to fly to Saturn had only to mail in a signed postcard. Signatures were cut out and scanned by the Planetary Society, then digitized and loaded onto a compact disk. After a national campaign roping in congressmen and canvassers, the grand result was 616,403 signatures on the carrier -- named, in high bureaucratic style-deaf fashion, the Digitized Versatile Disk.

My congressman, Christopher Cox, sent all his constituents a letter promising to funnel their names through his office and onto the Cassini spacecraft: "Your name will live on in space long after your grandchildren, and theirs, and theirs." They obtained some celebrity signatures from =Star Trek= actors and congressmen, baby footprints and pet paw prints.

The European Cassini collaborators got wind of all this and started their own signature collection. They took the signature diska step further and planned to sell a duplicate disk after the launch, reasoning that people who were to be immortalized on the interplanetary scale would, of course, want a copy. Like JPL, they set up a world wide web site to send names and messages. They got such memorable phrases as "Hello green worms," "HELP" and "Don't cry because you cannot see the sun, because the tears will stop you seeing the stars."

The Europeans never managed to get their hundred thousand signatures transmitted to JPL in time, so those are not on the Orbiter. Therefore the European Space Agency attached their own disk to the Huygens lander, while JPL's names fly on the Orbiter. The JPL team was uneasy about lack of screening of the ESA names and the European's plans to sell their disk commercially.

All this activity to collect a meaningless string of names and salutations emulates the portion of the Voyager record of least value, the list of Congressional committee members that NASA forced the Voyager team to include. The compact disk surely will not survive for more than a century or so, nor could it be easily read in any distant future. Even very clever humans or aliens could not figure out the encoding software from first principles, and should they, they would get only a list of indecipherable, disorganized names, and a few cryptic, disconnected messages in this sea of words.

One could imagine a far future discoverer wondering what to think of a species that created a message without attempting to make it "comprehensible, self-extracting, anti-coded, triply redundant, and graduated in content," as Lomberg summed up the Voyager and diamond disk approach. As a projection of pure vanity it resemblesthe International Star Registry, which sells people certificates stating that stars have been named for them. Such meaningless exercises in ego tell more about our species than we might like revealed.

This Kilroy disk had every sign of a hastily designed public relations stunt. Including long lists of names is a cliche of time capsules. Apparently the largest collection was the 22 million assembled to be buried at the order of President Ford for the bicentennial celebration in 1976 (and then stolen, a classic irony). As one engineer put it to me, knowing that I looked askance at the signature disk, he and others devoted eighteen months of hard work to produce a "heart-based signature disk," in contrast to the "mind-based diamond."

Of course, both gestures spring from a common impulse: to give people a sense of connection with something larger than themselves. To value the "heart" is to rank the expressive quality of deep time messages over their communicating ability.

My trouble with all such name-gathering was that the end result more nearly resembled the graffiti which disfigure many ancient monuments. After all, the scribblers upon the Parthenon no doubt felt some burst of elation, too, but the end result besmirched the work which is the point of it all.

Artist Jon Lomberg, principal designer of the Cassini disk, regretted that the signature disk would get commingled in the public mind with the actual message marker, vastly increasing the ratio of noise to signal, as engineers put it. Indeed, the Planetary Society has now made this a feature of their membership drives; in 1997 they attached a microchip to the Stardust mission to rendezvous with a comet. "And you'll be a part of it all," an advertisement promised.

We can expect that such masses of names will become a standard fixture of a publicity-conscious space program. The Mars Polar Orbiter of 1999 will carry a signature disk, instead of the Visions of Mars disk crafted earlier. This decision came from a NASA lawyer's worries over sending any copyrighted material, despite permissions already obtained.

Shouting at the stars may become commonplace. In 1998 the Sci-Fi Channel tried to arrange transmission of signature messages by radio beamed skyward. An entrepreneur tried to sell space on metal plates to be launched to the stars. None seems to have even thought about how utterly distinct life forms could say something understandable to each other.

Also in 1998 a French artist announced plans to launch a satellite on a long orbit to return in 50,000 years, bearing art and messages from our era. This "archeological bird" will feature moving solar panels that will make it look like it is flying. With shape-remembering metal, it could carry sculpture, too.

More adventurously, a firm advertized in 1998 plans to launch into interstellar space human hairs, at $50 a go. They anticipated getting several million customers who could send a hair sample (their DNA) and some small message as well. Perhaps bald men would feel left out, though there is nothing in the advertising circular that excludes body hair.

A similar offer envisions broadcasting people's names into interstellar space by microwaves, a garbage SETI message perhaps to be beamed to the Andromeda galaxy. The hunger for Kilroy gestures seems unbounded.

I fear that our time may be known in the longest sense by our graffiti, strewn over the entire solar system, and perhaps among the stars.

Copyright © 1999 by Abbenford Associates

Comments and objections to this column are welcome. Please send them to Gregory Benford, Physics Department, Univ. Calif., Irvine, CA 92717. email: gbenford@uci.edu