The Siege of Tyre is considered one of Alexander the Great's most brilliant military achievements. Tyre was a strategic Phoenician island city with walls reaching 150 feet high. Because the Tyrians refused to surrender and Alexander had no navy at the time, he ordered his army to build a massive causeway, or mole, from the mainland to the island. For seven months, his soldiers worked under constant fire to bridge the half-mile gap. When the Tyrians used fire ships to destroy the mole, Alexander simply built a wider one and eventually assembled a fleet of over 200 ships from conquered cities to blockade the harbor. Using ship-mounted catapults and siege towers, he finally breached the walls. The causeway permanently changed the geography of the region, turning the island of Tyre into a peninsula that remains connected to the mainland to this day.