Vandalian Tower

I am having trouble with my car and had to drive to Chichester this morning to get something sorted out. On my return journey I passed this ruin.
The romantic folly is on top of Tower Hill, not far from Harting, West Sussex. It was built in about 1770 by Sir Featherstonhaugh apparently to either commemorate the founding of Vandalia, a new American colony or his 21st Birthday.