Thanks to the movie “300” many people are familiar with the heroic stand of 300 Spartans at the Thermopylae against the invading Persian Army of 300’000. There were actually 6’700 other Greek soldiers fighting but the title “300” sounds sexier – it is Hollywood. The very same year, in 480 BC, the Athenians also defeated the much larger Persian Fleet at the Battle of Salamis. The Greek naval victory basically ended the Persian invasion. The mighty empire with 50 million people was beaten by a nation of only 1 – 2 million. Persia was big. It spanned a territory of 5.2 million square kilometres. In comparison, the size of the USA is 9.8 mio sq km or China is 9.6 mio sq km.
One of Xerxes' Pontoon Bridges Crossing the Hellespont (Dardanelles)
An empire of this size had resources that were beyond imagination. On his way from Asia Minor to Greece, the Persian Emperor Xerxes had to cross the Dardanelles (Hellespont) and follow the rocky coast from Thrace to Attica. His 650 galleys supported his army with food and anything else they needed. But most importantly, they helped crossing the Dardanelles. Not by ferrying troops across the 1.3 km wide straits, but by forming two pontoon bridges.
Xerxes' Empire in 480 BC was huge - it comprised 1/3 to 1/2 of the World's Population
The Greek historian Herodotus describes the undertaking in details. Born in 480 BC in Halicarnassus (Bodrum today), he was close enough to the events to listen to many direct eyewitnesses and compile a detailed account. During our first week of sailing, we are going to pass through the Dardanelles and will see firsthand how challenging the undertaking was. There is a north to south current of 1.3 miles/h. Not too strong for pontoon bridges but it would require lots of ropes to anchor the vessels.
View from the Canakkale Ferry to Kilitbahir Castle last
November - the Dardanelles here are 1'300 m wide
There are conflicting views of where the bridges were built and how they were built. Saw mills did not exist yet thus logs had to be made from splitting tree trunks. If the bridges were built around Canakkale, they would be 1’300 meters long. If built at the site of the ancient town Abydos, the distance would increase to 2’200 meters, if assembled even further east where the current is slower, we talk about 3’000 meters. Since 5-meter-wide warships were used and planks could not exceed 4 meter in length, a vessel plus plank cover eight meters only. The number of ships required was thus 150, 275 or 375 respectively. If Xerxes wanted to have two bridges, he would have to build them at the shorter crossings where the currents were stronger.
Model of a Persian Trireme - do not know on what Evidence this Model was built
Not an insurmountable problem but he would need strong anchors and ropes. According to today’s tables, a sail boat of 120 feet length needs a 30 kg anchor to remain stable in winds up to 30 km/h. Around 500 BC, mariners used mostly stone anchors which would have to be 2 – 3 times heavier since they could not hook into the sea floor. Heavy but still feasible. The 120 feet long boats then would need anchor ropes 5 to 7 times their length. For 275 vessels we get to 61 km of anchor rope or 122 km if two anchors were used. And of course twice the number for two bridges. Producing 244 km of anchor rope would have been a challenge – even for the Persian empire.
Be it as it may, the 300’000 Persian soldiers crossed the Dardanelles and marched onto Greece. Somehow, they made it work – even though we do not fully understand it anymore. The two bridges were later destroyed by a storm.
Xerxes' Invasion Route in 480 BC with more than 300'000 Soldiers
Tried to find out how long it took to build the pontoon bridges over the Dardanelles. But could not find anything. 2’400 years later, on 23 March 1945, the US 2nd Armoured Division built a pontoon bridge over the 300 m wide Rhine to push towards Berlin. It had about the same width as the Persian bridge. It took the 17th Engineer Battalion 6 ¼ hours to build it. Building something four times as long may have taken a day. It must have taken the Persians at least several days if not weeks to align their vessels and put on planks for the bridge.
The Rhein Pontoon Bridge the 17th Engineering Battalion built in 6 1/4 h on 23 March 1945
But Xerxes was not done yet with big engineering feats. He, or better, his soldiers and engineers, built a canal at the base of the Athos peninsula (where the monasteries are located), The canal's purpose was to avoid the stormy Cape Athos. It was 2’000 meters long, 30 meters wide and 3 meters deep which translates into 180’000 cubic meters. Digging up one cubic meter of soil takes a man 6 hours. We are talking thus about 1’080’000 man hours of work or 135’000 days (8 h day) or 450 men year (300 days of work). Guess the ground was not just loose and that not every-thing went to plan. The canal took 2 years to build.
Site of the Xerxes Canal - its Existence was doubted until 1990
Since the canal had no commercial use, it fell quickly in disrepair and was abandoned. Many people doubted the veracity of Herodotus’ account but in 1990 Greek and British Scientists found it again using modern geo-seismic tools and sedimentary analysis. If you know where to look you can still find it. But you need to know. It is not a tourist attraction. Why would the Greek maintain and excavate something their arch enemy built? The decision to let it dormant is understandable.
The Athos Peninsula seen from Space with a Simulation of the Xerxes Canal