The Martello Tower was a Genoese invention, initially utilized at Mortella Point on the island of Corsica. This relatively inexpensive method of fortification, a squat two-story tower armed with cannon, impressed the British in 1794 when the HMS Juno of 32 guns and the HMS Fortitude of 74 guns were ordered to reduce it to rubble. These ships cannonaded the tower for two hours, whereupon they were forced to retire, having been severely damaged by the tower's heated shot. "Hey," bellowed His Majesty's armed forces, "we should build some of these Martello Towers!" Great Britain went on to scatter the things all over the place for the next several decades.

But America didn't! The only other Martello Tower I've come across in my United Statesian starfort travels is Walbach Tower, just next to Fort Constitution at Portsmouth, New Hampshire...and that is a pile of rubble. Historically, however, Martello Towers were generally round, and without an expensive surrounding fact that was kind of the point of a Martello Tower, it existed as an inexpensive alternative to an actual fort. The Martellos built on Key West, therefore, are curiously American interpretations of the classic design.