 During the Interregnum , the castle continued to be used as a prison . Charles I could not be housed in the castle while en route to his imprisonment by Parliament at Carisbrooke Castle in 1647 because the facility was full , and he stayed at a local alehouse instead . The Royalist Sir William Davenant was imprisoned in Cowes during 1650 , writing the poem <unk> while incarcerated . As with East Cowes Castle , coastal erosion proved a particular problem for the fortification . An inspection in 1692 reported that the walls were cracked and at risk of collapse , and the antiquarian Francis Grose observed in 1785 that the castle was " strongly fenced with piles and planks " to prevent erosion from the sea . 
