The stretch of water known as Carrick Roads at the mouth of the River Fal was an important anchorage serving shipping arriving from the Atlantic and the Mediterranean. A small gun tower, called the Little Dennis Blockhouse, was built in 1539 overlooking the entrance, and plans were made to protect the anchorage further with five additional castles. In the event, only two of these were constructed, Pendennis and St Mawes Castle, positioned on each side of Carrick Roads and able to provide overlapping fire across the water. John Killigrew, a prominent member of the local Cornish gentry, probably oversaw the construction of Pendennis; it was built on his land and he was appointed as its first captain. Pendennis Castle cost £5,614 to construct.