In all Serbian lands conquered by the Ottomans, the native nobility was eliminated and the peasantry was enserfed to Ottoman rulers, while much of the clergy fled or were confined to the isolated monasteries. Under the Ottoman system, Serbs, as well as Christians, were considered an inferior class of people and subjected to heavy taxes, and a portion of the Serbian population experienced Islamization. Many Serbs were recruited during the devshirme system, a form of slavery in the Ottoman Empire, in which boys from Balkan Christian families were forcibly converted to Islam and trained for infantry units of the Ottoman army known as the Janissaries. The Serbian Patriarchate of Peć was extinguished in 1463, but reestablished in 1557, providing for limited continuation of Serbian cultural traditions within the Ottoman Empire, under the Millet system.