Southsea as a town, in historical terms, has had but a short history with its Henry VIII built Southsea Castle, as it is called, being made ready in 1544 and the first real housing in Grenada Road, the site of the Britannia Guest House not being built until 1885. However during the Civil War in 1642 the military governor of Portsmouth sided with the king and Parliament sent men to besiege Portsmouth. Southsea Castle was taken after some resistance and then the guns of Southsea Castle were then turned on the main town of Portsmouth. The siege was short lived and peace ensued without much loss of life.
Until the beginning of the 19th century Portsmouth consisted of Old Portsmouth and Portsea however in the early eighteen hundreds a new suburb began to grow outwards in the area to the south east of what is now known as Old Portsmouth. At first it was called Croxton Town after a Mr. Croxton but later it became known as Southsea after the castle. The first houses were built for skilled workers in the 'mineral' streets of Silver Street, Nickel Street and located to the south of the Kings Road.
Slightly later middle class houses were built in Kings Terrace and Hampshire Terrace but the new suburb remained small until 1835. Then it surged eastwards and by the 1860s the suburb of Southsea had grown along Clarendon Road as far as Granada Road, where the Britannia is located. In 1857 Southsea gained its own Improvement Commissioners responsible for paving, cleaning and lighting the streets.
Meanwhile St Jude's Church was built in 1851 by Thomas Ellis Owen who lived at Upper Mount House close to the Southsea shopping precinct of today and is now known as the Upper Mount House Hotel.
South of Southsea were two marshes. One the Little Morass stood near Old Portsmouth. It was drained in 1820-23 and the other and larger marsh, the Great Morass, existed south of Albert Road. It was not drained till the late 19th century.
The Crimean War obelisk was erected in 1857.
Lumps Fort was built at Southsea in 1869. However it was demolished at the end of World War One and is now the site of a model village close to the Britannia Guest House and on the other side of the boating lake.
For a time in the 1870s a boy named Rudyard Kipling lived in Campbell Road. Then in 1882 a doctor called Arthur Conan Doyle came to Southsea. He lived in Elm Grove and he wrote his first Sherlock Holmes story A study in Scarlet in Southsea. The comedian Peter Sellers was born in Southsea in 1925.
In 1885 a railway opened from Fratton to Southsea and the East Southsea Railway Station was situated in Granada Road, where the Britannia Guest House is located, but it was closed to passengers in 1914. There are no visible traces of the station or the lines existing to this day.