or Macedonians within their new city. A second attempt at negotiation resulted in Alexander's representatives being killed and then thrown from the walls into the sea. Alexander was enraged at the Tyrian defiance and ordered the siege to commence. The siege As Alexander could not attack the city from the sea, he built a kilometre-long two hundred foot wide(as claimed by Diodorus) causeway stretching out to the island on a natural land bridge no more than two meters deep. This causeway allowed his artillery to get in range of the walls, and is still there to this day, as it was made of stone. As the work came near the city walls, however, the water became much deeper, and the combined attacks from the walls and Tyrian navy made construction nearly impossible. Therefore, Alexander constructed two towers high and moved them to the end of the causeway. Like most of Alexander’s siege towers, these were moving artillery platforms, with catapults on the top to clear defenders off the walls, and ballista below to hurl rocks at the wall and attacking ships. The towers were made of wood, but were covered in rawhide to protect them from fire arrows. Although these towers were possibly the largest of their kind ever made, the Tyrians quickly devised a counter-attack. They used an old horse transport ship, filling it with dried branches, pitch, sulphur, and various other combustibles. They then hung cauldrons of oil from the masts, so that they would fall onto the deck once the masts burned through. They also weighed down the back of the ship so that the front rose above the water. They then set the ship on fire and ran it up onto the causeway. The fire spread quickly, engulfing both towers and other siege equipment that had been brought up. The Tyrian ships swarmed the pier, destroying any siege equipment that hadn’t caught fire, and driving off Macedonian crews who were trying to put out the fires. After this setback, Alexander was convinced that he would not be able to take Tyre without a navy. Fortunately for Alexander, his previous victory at Issus and subsequent conquests of the Phoenician city states of Byblos, Arwad and Sidon had meant that the fleets of these cities, which had composed most of the Persian navy, came under his banner. This immediately gave him command of a fleet of 80 ships.