On the 27th of October, Belgrade Fortress becomes an open-air church. Hundreds of people silently flock to Donji grad while the bells of the Church of the Ružica echo over the Sava and the Danube. This is what Belgrade does to pay homage to its patron saint, Saint Petka, to drink the water of her miraculous origin in a small chapel beneath a strong defensive wall. The remains of the Immaculate Mother of Paraskeva, or Sveta Petka as she is known in Belgrade, were brought to the city by a ship along the two rivers in the 15th century. This pious woman of Slovene origin was born in the 10th century in the Byzantine castle of Epivat, a day's walk from Istanbul. From her early youth she devoted herself to God and prayer, living as a hermitess in the greatest asceticism.

When she passed away in the 11th century, miracles began to occure at her tomb, and the saint's earthly remains were transferred to the Church of the Holy Apostles at the Castle of Kalikratija on the Sea of Marmara. Even then, Saint Petka attracted hundreds of pilgrims. Meanwhile, the crusaders and the Ottomans intented to conquer the Byzantine territories and provoked the unusual journey of Saint Petka's relics through the Orthodox lands. In the 13th century they were sent to Trnovo - the capital of the Bugarian Tsardom. When the Ottomans took over the castle, the relics were transported to Vidin in 1393, and after the fall of Vidin to Serbia: first to Kruševac, and then finally to Belgrade.