Pitt was the Lord Warden of the Cinque Ports when Napoleon threatened to invade Britain and began to amass an army of 150,000 men, barges and ships at Boulogne. In preparation for this possible invasion the construction of the string of 74 small "forts" was approved. Later, there was also a further 29 towers built on the East Coast of Essex and Suffolk but those towers are outside the scope of this site.
A report in the Monthly Mirror of September, 1805 stated:
Gradually, I will try to add pictures of the remaining Kent towers. This is the current list:
Spread along the South Kent coast into Sussex is a line of small defensive forts built at the time of the Napoleonic Wars known as the Martello Towers. The model for the towers was a round fortress at Mortella Point in Corsica, which, in 1794, had beaten off the attack of two British Warships, HMS Fortitude [74 guns] and HMS Juno [32 guns] but was eventually defeated by land based forces after two days of heavy fighting. Scetches and plans were subsequently used in 1803 by a military engineer, Captain William Ford, to propose a chain of such structures to defend the South Coast against possible invasion.
"The martello towers are at length begun to be adopted by the Government in the neighbourhood of Folkestone. Four of them are in great forwardness, within a quarter of a mile of the town, just at the bottom of the hill, where they command the beach, and cross each other at right angles, so as to produce great havoc on an invading army".
There are several of the Towers still standing and the best examples I know of are at Dymchurch. Martello Tower No. 24 has been restored to its original condition and is now an English Heritage site.