The early port settlement of Plymouth, called "Sutton", approximates to the area now referred to as the Barbican and has 100 listed buildings and the largest concentration of cobbled streets in Britain. The Pilgrim Fathers left for the New World in 1620 near the commemorative Mayflower Steps in Sutton Pool. Also on Sutton Pool is the National Marine Aquarium which displays 400 marine species and includes Britain's deepest aquarium tank.