Hurst Castle is an artillery fort established by Henry VIII on the Hurst Spit in Hampshire, between 1541 and 1544. It formed part of the King’s Device program to protect against invasion from France and the Holy Roman Empire, and defended the western entrance to the Solent waterway. The early castle had a central keep and three bastions, and in 1547 was equipped with 26 guns. It was expensive to operate due to its size, but it formed one of the most powerful forts along the coast. During the English Civil War of the 1640s, Hurst was held by Parliament and was used briefly to detain King Charles I before his execution in 1648. It continued in use during the 18th century but fell into disrepair, the spit being frequented by smugglers.