Southsea Castle | The Mary Rose
Southsea Castle
Historical | 18 Sep, 2023 | Museum Blogger
The history of Henry VIII’s castle by the sea

Southsea Castle has a special place in the history of the Mary Rose – It was from here that Henry VIII witnessed the sinking of his favourite warship, and the first exhibition of objects recovered from the wreck was held within the castle keep. But what’s the full story behind this historic landmark of Portsmouth seafront?

Castle Origins

Southsea Castle's story begins in the 16th century, during the reign of Henry VIII. As tensions escalated between England and continental Europe, the threat of invasion loomed large. In response, Henry began to fortify England's coastline against potential attackers. Completed in 1544, Southsea Castle was one of the key components of this coastal defence strategy.

The castle's strategic location at the entrance to Portsmouth Harbour made it an ideal site for monitoring and controlling maritime traffic. Its stone walls and gun emplacements were designed to deter enemy ships and protect the valuable harbour. The castle's enduring architectural elements are a testament to the engineering prowess of the time.

It was only one year later, in 1545, that Southsea Castle saw combat (of sorts) for the first time, as in July a large French invasion fleet arrived off the coast of the Isle of Wight. Other than a short skirmish at sea that saw the loss of the Mary Rose, most of the fighting took place on the Isle of Wight, so Southsea Castle didn’t take part in the fighting, but it is featured prominently in the Cowdray Engraving, a copy of a long-lost painting showing the Battle of the Solent.

The English Civil War

Henry VIII wasn’t the only king associated with the castle; in the 17th Century, the castle's garrison remained under Royalist control for the early years of the Civil War, loyal to Charles I. This presented a challenge to the Parliamentarians, who sought to exert their influence over the castle and the surrounding area.

In 1642, as tensions escalated, Parliamentarian forces under the command of Sir William Waller launched a campaign to capture strategic locations along the southern coast, including Southsea Castle. They recognised the significance of gaining control over this coastal fortress, as it would help secure their maritime communications and disrupt Royalist activities in the region.

The siege of Southsea Castle began in earnest in July 1642, with Parliamentarian forces launching a determined effort to take control of the stronghold. In October 1642, after enduring a gruelling siege that had lasted for over three months, the Royalist garrison at Southsea Castle finally surrendered.

The capture of the castle marked a significant victory for the Parliamentarians, as it further solidified their control over the strategic southern coast and bolstered their military and political position. The aftermath of the capture saw the Parliamentarians reconfiguring the castle to better serve their needs. The fortifications were enhanced, and the castle's role as a coastal defence stronghold was reinforced.

Image Portsmouth Museums Services

An explosive incident

Southsea Castle was struck by disaster in 1759, when a relative of one of the castle soldiers lit a cooking fire in their room at the castle. It’s possible that they were unaware that their quarters were located above the powder store, but they soon became very aware when sparks from the fire fell through the floorboards, igniting the gunpowder and causing an explosion that destroyed part of the castle and killed 17 people.

The damage was so severe that the castle was considered for demolition, but imminent war with France meant that England's defences needed to be in place, so the castle was instead repaired.

The 19th Century - Restoration, Incarceration and Navigation

As the 19th century unfolded, the strategic significance of Southsea Castle in terms of traditional coastal defence diminished. The emergence of new military technologies and changing geopolitical dynamics shifted the focus away from castle-like fortifications. However, Southsea Castle's legacy was far from over.

In the mid-1800s, the castle underwent a transformation to adapt to modern military needs. Southsea Castle was restored and repurposed, becoming a military storehouse and arsenal. Its storerooms were converted into casemates for artillery, reflecting the changing role of coastal fortifications. The castle's robust architecture made it a suitable location for storing munitions, arms, and supplies that were crucial for the British military during this era of rapid technological advancement.

Southsea Castle's role in the 19th century wasn't limited to its military functions. During the Napoleonic wars the castle served as a prison for captured French soldiers and sailors, and in 1828 a lighthouse was constructed on the northwest wall of Southsea Castle. Its light, initially powered by oil lamps and later electrified, aided ships traversing the often-perilous waters of the English Channel.

image from wikimedia commons

World Wars and Modern Warfare

The 20th century brought with it unprecedented challenges and conflicts that would once again thrust Southsea Castle into the centre of historical events. Both World War I and World War II saw the castle serving a vital role in Britain's defence strategy.

During World War I, Southsea Castle played a role in safeguarding the coast and monitoring maritime activities. Its vantage point provided a clear view of the English Channel, and its gun emplacements were manned to defend against potential naval threats. 

In World War II, Southsea Castle once again became a key asset. The threat of German invasion loomed, and the castle was transformed into a coastal defence stronghold. Its gun emplacements were reactivated, and the castle's strategic location offered a valuable line of defence against enemy forces.

The castle's role as a military asset during these conflicts reflected its enduring importance as a maritime fortress.

Southsea Castle Today

In the post-war period, as military strategies evolved and technological advancements altered the nature of warfare, Southsea Castle's military function diminished, and in 1960 the castle was sold off to Portsmouth City Council.

Today, Southsea Castle is a popular tourist attraction, and stands as a living testament to England's maritime heritage, its historical significance and architectural charm continuing to capture the imagination of locals and visitors alike.