It was a natural anchorage used by the Romans which has been changed into an artificial harbour that is now the island's main port for passengers.
[2] In 1605, a Royal Charter authorised a pettie Custume tax on imports to Guernsey to pay for harbour development.
Since 1881 the harbour has housed the Saint Peter Port Lifeboat Station, originally in a building on the Castle Pier.
The First World War saw the establishment of a French seaplane base, on the pier close to Castle Cornet.
[6] On 28 June 1940, German commanders sent a squadron of bombers over the islands and bombed the harbours of Guernsey and Jersey.
In St Peter Port some lorries lined up to unload tomatoes for export to England were mistaken by the reconnaissance for troop carriers.
No damage was caused to the submarine; escorting vessels were not so lucky, where the rockets hit a Dutch coaster M.V.
The Nazi German forces improved the defences of the harbour including building a number of steel and concrete bunkers and casemates, most of which are located on the Castle pier.
The southern arm of the original harbour going east from near the Town Church was originally a mole, referred to in 1275 by Edward I of England when it was mentioned as needing reconstruction, given permission to raise a local tax to cover the cost, little was done until a dry stone pier, was constructed by 1580.
[11]: 189 The northern arm of the original harbour heads east from the Quay, with a retaining pier for the Careening Hard going north.
Originally built from 1703 as a breakwater, gradually improved and by 1750 was completed as a dry construction with an arm heading south east.
[9][2]: 2 The harbour quay was completed by the late 1770s, prior to that everything was landed on the beach, cattle still being made to swim ashore.
The smaller original 1975 Albert Marina, located between the Castle and Albert piers and the newer Queen Elizabeth II Marina located north of the St Julian's Pier which was opened by Queen Elizabeth II in 1989.