Civil War

During the English Civil War 1642-1649 the Square Tower was used as an arsenal and contained large amounts of gunpowder and munitions. The Town of Portsmouth was under siege with the Royalist forces trapped inside the town by the Roundheads. As a last bargaining chip the Royalist Governor of Portsmouth Colonel Goring threatened to blow up the tower and its munitions, unless the terms of his own surrender were agreed to. 

The Roundheads agreed to his terms, allowing him to board ship in the harbour. However in a final act of defiance Goring took the key to the tower with him and threw it overboard into Portsmouth harbour. During the 1850s the key was dredged up from the harbour and was displayed, before it's destruction in the Guildhall Museum, it's whereabouts or even it's existence at all is now unknown.

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Powder Bridge

In 1716 the tower was deemed as unsuitable as a magazine on safety grounds. The gunpowder from the tower had to be transported along the streets to the loading berth at Portsmouth Point. The shaking of the barrels along the uneven streets left trails of gunpowder along the route, a popular part of town frequented by drunken smoking sailors, the threat of explosion was a real possibility as the tower could hold up to 6000 barrels of gunpowder at a time. 

To rectify this problem a jetty was built adjacent to the tower, which became known as 'Powder Bridge', this occupied the position where Victoria Pier now stands. The new jetty allowed the gunpowder to be loaded directly from the magazine, through an opening in the sea wall along the jetty to the moored ships. The brickwork lining the tower was probably added at this time to try and prevent the damp in the tower, it is claimed that the spring tides came into the ground floor under the foundations, water can still be seen inside the lowest part of the tower today.

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Naval Meat Store

In 1779 the admiralty wanted to build a new victualling store at the town quay, however this was not feasible as it would have masked one of the towns batteries, the square tower was offered as an alternative, so the tower became a meat store and operated in conjunction with a newly erected slaughter house nearby. The old 'Powder Bridge' now became known as the 'Beef stage'.

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Semaphore Tower

In 1823 the admiralty added a semaphore station on top of the tower to carry messages from the shore to ships in harbour and at sea. The first of a chain linking Portsmouth with the admiralty in London. The semaphore system subsequently became redundant with the introduction of the electric telegraph system and the semaphore tower was demolished in 1848. 

On the outside of the building the original gun ports and windows were blocked up when the tower became a magazine and these features disappeared completely when the tower was refaced with stone in 1827. 

The sea defences at Old Portsmouth from the King's Bastion to the Round Tower were reorganised and improved in the period from 1848-50. The Square Tower was returned to the Board of Ordanance and during this improvement work the top of the tower was reinforced and three 8" inch guns were installed, the emplacements for these guns are still evident today.

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King Charles

On the north side of the tower, looking up the High Street, a bust of Charles 1st is mounted. The bust was made by Hubrecht le Seur and was presented to the town by the King in 1635. The inscription reads "After his travels through all of France into Spain, and having passed very many dangers both by sea and land, he arrived here the 5th day of October 1623" it originally ended "there was the greatest applause of joy for his safety throughout the Kingdom that was ever known or heard of." The inscription appears to have been damaged early in the 19th century, possibly in 1827 when the tower was repaired.