Portsmouth (England), city and unitary authority, southern England, occupying Portsea Island and located on the Solent, the channel separating the Isle of Wight and the southern coast of England. Portsmouth is one of the most important naval stations in the United Kingdom. The city has some commercial wharves, and passenger traffic flows from here to the Continent. The Southsea section of the city is a popular seaside resort.

Portsmouth contains a number of historical structures. Portchester Castle dates from the 3rd century ad, when the Romans first built a defensive structure here. The castle was later expanded and used by English kings during the Middle Ages. The Cathedral of Saint Thomas dates from the 12th century. Three noteworthy ships are located here: the hull of the Mary Rose, the flagship of King Henry VIII, which sank in 1545 as the king watched; the HMS Victory, which was the flagship of Admiral Horatio Nelson at the Battle of Trafalgar (1805); and the HMS Warrior, which dates from 1860 and was Britain’s first armored battleship. The house in which novelist Charles Dickens was born in 1812 is located in Portsmouth and is now a museum. The University of Portsmouth is also here.

Portsmouth was founded in 1194 by Richard I. In 1496 the Royal Dockyard was established, and the world's first dry dock was built here. During World War II (1939-1945), because of its strategic military significance, Portsmouth was damaged by extensive German aerial bombings. City population 190,370 (1996 estimate).