In 1499, the Sultan Vagjazit II took over Nafpaktos from the Venetians. He ordered the fortification of Rio-Antirio (you find a fortress on both sides of the bridge), which he called the small Dardanelles. From here, he could control the entrance and exit traffic of the gulf since there was no Canal of Corinth yet! He chose this spot from the same reason as the engineers chose this spot to build the bridge. Here, the gulf is at its narrowest.