Alexander's siege of the city of Tyre is one of the better known battles of Alexander's dynamic conquest of the Persian Empire. There was an old Phoenician city of Tyre, but it was considered to exposed to attacks from larger empires, like the Assyrians and Persians. So the citizens of Tyre built a "New Tyre" on an island close to the coast of Phoenicia. It was considered to be an impregnable fortress. Alexander had to lay siege from January to July 332 BC and build a mole (a causeway of stone blocks) from the coast out to the island fortress. This battle has been described in many books about Alexander the Great, warfare in Classical Antiquity or books about the Phoenicians. A good short summary of this battle can be found here. http://www.ancient.eu.com/article/107/