An important seaport of South Hampshire, 79 m. SW. of London, situated on a small peninsula at the head of Southampton Water (a fine inlet, 11 m. by 2), between the mouths of the Itchen (E.) and the Test (W.); portions of the old town-walls and four gateways still remain; is the head-quarters of the Ordnance Survey; has splendid docks, and is an important steam-packet station for the West Indies, Brazil, and South Africa; yacht and ship building and engine-making are flourishing industries.