The town was fortified between the years 1520 and 1566, and the wooden bridge rebuilt in stone. The stone bridge, the Old Bridge ("Stari most"), was erected in 1566 on the orders of Sultan Suleiman the Magnificent and at long and high, quickly became a wonder in its own time. Later becoming the city's symbol, the Old Bridge was designed by Mimar Hayruddin, a student and apprentice of Ottoman architect Mimar Sinan. In the late 16th century, Köprühisar was one of the towns of the Sanjak of Herzegovina. The traveler Evliya Çelebi wrote in the 17th century that: "the bridge is like a rainbow arch soaring up to the skies, extending from one cliff to the other... I, a poor and miserable slave of Allah, have passed through 16 countries, but I have never seen such a high bridge. It is thrown from rock to rock as high as the sky."