to take the town by force. His engineers didn't believe it would be possible to build such a massive structure, and so Alexander sent peace envoys once more to propose an alliance. The Tyrians believed this to be a sign of weakness, and so they killed the envoys and threw their bodies over the city wall. The dissent against Alexander's plans to take the city by force disappeared, and his engineers began to design the structure. Alexander began with an engineering feat that shows the true extent of his brilliance; as he could not attack the city from sea, he built a kilometer-long causeway stretching out to the island on a natural land bridge no more than two meters deep. Alexander then constructed two towers 150 feet high and moved them to the end of the causeway. The Tyrians, however, quickly devised a counterattack. They used an old horse transport ship, filling it with dried branches, pitch, sulfur, and various other combustibles. They then lit it on fire, creating what we might call a primitive form of napalm, and ran it up onto the causeway. The fire spread quickly, engulfing both towers and other siege equipment that had been brought up. This convinced Alexander that he would be unable to take Tyre without a navy. Fate would soon provide him with one. Presently, the Persian navy returned to find their home cities under Alexander's control. Since their allegiance was to their city, they were therefore Alexander's. He now had eighty ships. This coincided with the arrival of another hundred and twenty from Cyprus, which had heard of his victories and wished to join him. Alexander then sailed on Tyre and quickly blockaded both ports with his superior numbers. He had several of the slower galleys, and a few barges, refit with battering rams, the only known case of battering rams being used on ships. Alexander started testing the wall at various points with his rams, until he made a small breach in the south end of the island. He then coordinated an attack across the breach with a bombardment from all sides by his navy. Once his troops forced their way into the city, they easily overtook the garrison, and quickly captured the city. Those citizens that took shelter in the temple of Heracles were pardoned by Alexander. It is said that Alexander was so enraged at the Tyrians' defense