Round Tower Portsmouth: The 1415 Fort Facing Fort Blockhouse

What is Round Tower Portsmouth?

Round Tower Portsmouth is a fortification at the entrance to Portsmouth Harbour. It is a Grade I listed building, positioned where its defences helped protect the harbour entrance and the approach to England.

The tower was not an isolated defence. Across the water, Fort Blockhouse occupied the opposite side of the entrance, creating the two-sided arrangement that made this location strategically important. The RULE PORTSMOUTH! tour visits Round Tower as one of its stops and places the fortification within Portsmouth's harbour defences.

If you are planning a harbour walk with a companion, this is the detail worth sharing: the story is not only about one tower, but about why both sides of the entrance mattered.

When was the Round Tower built?

Round Tower was first completed in 1415, and the tour material associates it with Henry Vth. That was the year of Henry V's victory at Agincourt in France, placing the tower's early history in a period shaped by conflict with France.

The tower's purpose was tied to that wider defensive concern. Portsmouth Harbour needed protection from attack, and the harbour entrance was described as an ideal defensive position. From Round Tower, the fortification formed part of the measures intended to defend the entrance to Portsmouth Harbour and, in turn, England.

How did the Round Tower help defend Portsmouth Harbour?

Round Tower and Fort Blockhouse formed opposing sides of a defensive pinch securing the entrance to Portsmouth Harbour. Fort Blockhouse, across the water, was started in 1431, giving the two fortifications a related role on either side of the approach.

The battery in its present form was rebuilt by the Dutchman Bernard de Gomme in the late 17th century. That later rebuilding is part of the place's documented defensive history, but the essential relationship remains the same: Round Tower stood on one side of the entrance while Fort Blockhouse stood across the water.

The tour's challenge captures the urgency built into that position: get to the cannon before the ships reach the harbour. To understand the arrangement at the harbour entrance rather than as an isolated building, see Round Tower in person through the RULE PORTSMOUTH! route.