Built between 1720 and 1725, this huge square retains only rare samples of its 18C Georgian architecture. At No. 9, in 1785, lived the first American ambassador to London, John Adams, later President of the United States. Opposite is a memorial to the American squadrons of the Royal Air Force during the Second World War. On the west side of the square is the massive American Embassy building (designed by Eero Saarinen).