The massive 16th and 17th-century Spanish fortifications guarding Old San Juan Harbor — Castillo San Felipe del Morro (El Morro) on the western headland and Castillo San Cristóbal on the landward approach — represent the most complete colonial-era defense system in the Western Hemisphere, with walls up to 20 feet thick and rising 140 feet above the sea. The fortifications repelled attacks by Francis Drake in 1595 and the Earl of Cumberland in 1598 and remained active military installations through the Spanish-American War.