Located next to the sea, it is believed that the first fortification sited on the bar of the River Lima estuary dates from the reign of King Afonso III (13th century). However, the earliest certain date is the 15th century, when a fortress was built there that would have been completed in the following century, in the reign of King Manuel I. This is indicated by various Manueline architectural features, notably the 'Roqueta Tower' in the south-west bastion of the present fortress.
In the late 16th century, the fortress underwent a series of improvement works, having already been under Spanish domination in the reign of Philip II (Philip I of Portugal). And so the current fortress, with its polygonal floor plan, was built based on a design by Filippo de Terzi, the most famous architect of military buildings of that period.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.