 However, Mary of Guise's forces continued to advance, once again threatening St. Andrews.The situation was transformed by the arrival of the English fleet in the Firth of Forth in January 1560, and the French retreated to the stronghold of Leith near Edinburgh.The English and the Lords agreed further support by the Treaty of Berwick in February 1560 and an English army crossed the border to lay siege to the French in Leith.