ATHENS (National Geographic) – Persian engineering prowess is evident in the fortifications at Babylon and Ecbatana as well as in the bridges across major rivers. The pontoon bridges crossed by Xerxes’ army over the Dardanelles Strait in 480 B.C. were the fruit of the empire’s long experience in infrastructure projects. Herodotus recounts how almost 700 ships were lined up in parallel rows to span the strait, which is slightly more than one mile across. The boats—triremes from the Persian fleet and civilian craft from nearby towns—were tied to each other with ropes made of flax, papyrus, and Phoenician linen, pulled taut by windlasses positioned on the shore. After the boats spanned the strait, wooden walkways were laid across their decks, lined with a thick layer of packed earth to prevent slippage. Finally, palisades were erected along the sides of each pontoon to prevent the horses from being frightened by the sight of the sea. The bridge was as much a statement of Persian power as any piece of military infrastructure. The strait represented a profound regional symbol to the Greeks. According to Greek mythology, it is here that the twin siblings, Phrixus and Helle, are saved from their murderous stepmother by a magical golden ram that ferries them across the strait (in some versions of the tale, the ram swims while in others it flies). Helle, however, falls off the ram’s back and drowns, which is why the strait in antiquity was known as the Hellespont—Sea of Helle.
For a decade, researchers on the site used methods typical of oil and mining prospecting, including seismic tests and refraction and reflection techniques. With heavy hammers they struck metal pieces embedded in the ground. They then used geo-phones to record the strength and direction of the impulses generated. They calculated the depth of subsoil layers by measuring the time for the volumetric waves to pass through them. They then linked subterranean points that showed similar acoustic transmission. They also performed electrical discharge and georadar (GPR) tests to get a clearer picture of how the canal was structured.
Radiocarbon dating of the organic elements and high-resolution satellite images were definitive. Using their findings, the researchers created a three-dimensional digital representation of the canal. The Greek-British joint project proved not only that some kind of channel had existed there but also settled the contentious issue of whether it could have run all the way from one coast to the other.
At first, the team had shared the doubts of generations of skeptics who believed a channel could not have been cut across the rocky southern part of the peninsula. But the discovery of the channel bed, the measurements made through seismic waves, and the stratigraphic analysis of the subsoil told a different story. The team also confirmed the channel had been constructed with sloping sides and measurements aligned with those of Herodotus’s description: “from sea to sea, wide enough to float two triremes rowed abreast.” Since the bottom of the channel turned out to be as wide as 50 feet, with the outward sloping walls the navigable space at the surface indeed would have reached the width necessary for two triremes to row abreast.
Having proved the canal’s existence, researchers still ponder the question of why the Xerxes Canal disappeared, both in its physical from and—apart from Herodotus’s account—from Greek memory. No marine remains, such as shells, have shown up in the sediments on the canal bed, suggesting that the channel was filled with seawater for only a short period of time.
The size of the canal was not amendable to larger trading vessels, so it appears it was used only for smaller military ships. There is, however, a plausible theory as to why this infrastructure disappeared relatively quickly: In 479 B.C., the Persian forces were defeated at the Battle of Plataea, and the inhabitants of the Mount Athos Peninsula were freed from the Persian yoke. It follows that they might allow an enemy-built canal to silt up naturally, or even fill it in themselves, thereby obliterating the landmark that symbolized their oppression. (Concluded)