Portsmouth ( ) is a port and city in the ceremonial county of Hampshire in southern England. The city of Portsmouth has been a unitary authority since 1 April 1997 and is administered by Portsmouth City Council. Portsmouth is the most densely populated city in the United Kingdom, with a population last recorded at 208,100. Portsmouth is located south-west of London and south-east of Southampton. Portsmouth is mostly located on Portsea Island; the only English city not on the mainland of Great Britain. Portsea Island has the third highest population in the British Isles after the islands of Great Britain and Ireland. Portsmouth also forms part of the regional South Hampshire conurbation, which includes the city of Southampton and the boroughs of Eastleigh, Fareham, Gosport, Havant and Waterlooville. Portsmouth is one of the world's best known ports, its history can be traced to Roman times and has been a significant Royal Navy dockyard and base for centuries. Portsmouth was first established as a town with a royal charter on 2 May 1194. Portsmouth was England's first line of defence during an attempted French invasion in 1545 at the Battle of the Solent, famously notable for the sinking of the carrack Mary Rose and witnessed by King Henry VIII of England from Southsea Castle. Portsmouth has the world's oldest dry dock, "The Great Stone Dock"; originally built in 1698, rebuilt in 1769 and presently known as "No.5 Dock". The world's first mass production line was established at the naval base's Block Mills which produced pulley blocks for the Royal Navy fleet. By the early-19th century, Portsmouth was the most heavily fortified city in the world, and was considered "the world's greatest naval port" at the height of the British Empire throughout Pax Britannica. By 1859, a ring of defensive land and sea forts, known as the Palmerston Forts had been built around Portsmouth in anticipation of an invasion from continental Europe. In the 20th century, Portsmouth achieved city status on 21 April 1926. During the Second World War, the city was a pivotal embarkation point for the D-Day landings and was bombed extensively in the Portsmouth Blitz, which resulted in the deaths of 930 people. In 1982, a large Royal Navy task force departed from Portsmouth for the Falklands War. Her Majesty's Yacht Britannia was formerly based in Portsmouth and oversaw the transfer of Hong Kong in 1997, after which Britannia