As tensions between the United Kingdom and the United States, as well as fears of further rebellion in British North America, grew in the late 18th century, the British reinforced the defences of their colonies according to a plan drawn up in the 1790s by Gother Mann. The ramparts around the Upper Town cliff and four martello towers (still extant) on the Plains of Abraham were completed before 1812. A citadel was a key part of Mann's design, but no fort was built because the cost was deemed prohibitive.