Portsmouth was founded about 1180 when a merchant called Jean De Gisors founded a little town in South-West corner of Portsea Island. Jean De Gisors was a merchant who owned a fleet of ships. He was also a landowner who owned land on Portsea Island. In the Southwest of the island was a small inlet from the sea called the Camber. It was a sheltered place for ships to land and De Gisors decided it was an ideal place to start a town.
De Gisors divided up the land into plots for building houses and he started a market. Craftsmen and merchants came to live in the new settlement. In 1185 a parish church was built (in the 20th century it became Portsmouth Cathedral).
In 1194 the king gave Portsmouth a charter. (A document granting the townspeople certain rights).
By the early 13th century Portsmouth was described as 'one of our most important ports'. However the population of Portsmouth was probably only about 1,200 people. The main exports from Medieval Portsmouth were wool and grain. The main imports were wine, woad for dyeing, wax for candles and iron.
In 1212 a building called the Domus Dei (house of God) was built at Portsmouth. It was a hospice for pilgrims. There was also a hostel for lepers outside the town. Portsmouth was, at first, run by a man called a reeve assisted by bailiffs. By the 14th century Portsmouth had a mayor elected by the merchants. There were also constables responsible for arresting wrongdoers.
In 1369 a military governor was appointed who was responsible for the defence of the town. However Portsmouth was burned down 4 times during the 14th century during a period of almost continuous warfare between England and France. The French burned Portsmouth in 1338, 1369, 1377 and 1380, (This was easy as most of the buildings were of wood with thatched roofs. On the other hand they could be easily rebuilt).
Portsmouth was not fortified till after the last attack in 1380. It was given wooden walls. Then about 1418 a tower was erected at the entrance of Portsmouth Harbour called the Round Tower. Cannons on it could fire at any enemy ship attempting to enter the harbour. In the 16th century a giant chain was stretched across the mouth of the harbour. The winch was by the Round Tower. The chain could be lowered to let in friendly ships but raised to prevent enemy ones entering the harbour.