century, the Sarajevo Haggadah came to Sarajevo along with Jewish refugees from Andalusia. For the first time in its history, Sarajevo was the city of four religions. The Jewish population made note of this, naming the city "The European Jerusalem." Under the leadership of Gazi Husrev-beg, a major donor who was also responsible for most of what is now the Old Town, Sarajevo grew at a rapid rate. Sarajevo became known for its large marketplace and numerous mosques, which by the middle of the 16th century numbered over a hundred. Numerous other buildings appeared, including religious schools, such as the school of Sufi philosophy. Gazi Husrev-Beg himself established a number of buildings named in his honor, such as the Sarajevo library which, in its prime, was in the same category as the Madrassa of Beyazid II. Gazi Husrev-Beg also built the city's clock tower (Sahat Kula). Sarajevo became one of the most advanced cities in Europe. It had its own water system, clock tower, bathhouses, and schools. In a time when education was merely for the wealthy, and most Europeans considered baths to be unhealthy, Sarayliyas (Sa-ray-lee-yas, residents of Sarajevo) were among the cleanest and most culturally advanced commoners on the continent. A famous Sarajevan poet of the time wrote, "There it seems to man that he can live for a long time, for in a thousand places in Sarajevo flows water from the well of longevity." At its height, Sarajevo was the biggest and most important Ottoman city in the Balkans after Istanbul itself. By 1660, the population of Sarajevo was estimated to be over 80,000. Comparatively, Belgrade in 1838 had a mere 12,963 inhabitants, and Zagreb as late as 1851 had only 14,000 people. This period of early Ottoman rule will be long remembered as Sarajevo's golden age. The 16th century was its peak, when nearly the whole city area (that would last until the late 19th century) was built. During the 17th century, Sarajevo didn't expand, although its population continued to grow. Its residents lived luxuriously, and Sarajevo was the richest city in the West Balkans after Dubrovnik. However the 17th century also brought the start of the decline of the Ottoman Empire. With the defeats at Vienna, the empire grew weaker, and along with the empire as a whole did its various regions. Although Sarajevo would remain prosperous until the very end of the 17th century,