How was alexander able to conquer a city of high walls on an island.

Alexander's request was simple: he wished to sacrifice to Heracles in Tyre. (The Phoenician god Melqart was roughly the equivalent of the Greek Heracles.) The Tyrian's recognised this as a Macedonian ploy to occupy the city and refused, saying instead that Alexander was welcome to sacrifice to Heracles in old Tyre, which was built upon the mainland. Old Tyre held no strategic importance - it was undefended and the Tyrian navy was stationed in the harbours of new Tyre.

The Tyrian refusal to capitulate to Alexander's wishes was tantamount to a declaration of war. But, despite the youthful Alexander's growing reputation, the Tyrians had every reason to be confident. In addition to a powerful navy and mercenary army, their city lay roughly half a mile (0.8 km) offshore, and, according to the account of the historian Arrian, the walls facing the landward side towered to an impressive 150 ft (46m) in height. Whether they actually stood that high is doubtful and open to debate, but even so, the defences of Tyre were formidable and had withstood a number of mighty sieges in the past. The Tyrians began their preparations and evacuated most of the women and children to their colony at Carthage, leaving behind perhaps 40,000 people. Carthage also promised to send more ships and soldiers.

Alexander was aware of Tyre's supposed impregnability and convened a council of war, explaining to his generals the vital importance of securing all Phoenician cities before advancing on Egypt. Tyre was a stronghold for the Persian fleet and could not be left behind to threaten Alexander's rear. In a last-ditch attempt to prevent a long and exhaustive siege, he despatched heralds to Tyre demanding their surrender, but the Macedonian's were executed and their bodies hurled into the sea.