All the Serbian rulers were very religious and instead of building palaces, they established monasteries as their endowments and mausoleums. Monasteries used to be the place where important decisions were made. The first books were copied here and thus literacy was spread and the culture of the Serbian people was formed. The walls were illuminated by frescoes reflecting the artistic styles of the time. Some of this frescoes are extremely valuable art treasures like the frescoes in the Sopocani monastery and the Frescoe of the White Angel ("Beli anđeo") from the 13th century in the Monastery of Mileševa now under the protection of
UNESCO. Dečani Monastery, Patriarchate of Peć, Gračanica Monastery, and Our Lady of Ljeviš are also listed in
UNESCO World Heritage Site list.