Porto Palermo Castle was probably built by the Venetians as it could be relieved by sea and it has the same triangular plan with round towers found in the Venetian fort at Butrint. At that time the identity of its builders ought to have been clear, from a plaque above the entrance gate. This plaque is now missing but the weathering of the stones clearly shows that it has not been missing for many decades. Almost certainly this plaque had a carving of the lion of St. Mark. The most plausible explanation of the error found in the guide books is a rewriting of history in the communist period. Re-ascribing a colonial legacy to construction by an Albanian fits a nationalist isolationist agenda.
The castle would have been vulnerable to cannon fire from the hill above and this also suggests an early date for its construction when cannon had not developed the range they had later. In 1662 the Venetians feared the Turks would recondition it. In 1803 Ali Pasha offered the castle and port to the Royal Navy. At which time the fort only had 4 or 5 cannon implying that Ali Pasha did not see the fort as important for him.
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.