1937, when the Chapel of Saint Petka, the porch and the clergy house were completed. They were all designed by the architect Momir Korunović. Still, many believe that the chapel is older than the church. Small niche, which surrounded the walled spring before the proper chapel was finished, used to be called Zemun's Chapel, though the reason for this name is not known. It was during this works that an ossuary of the World War I defenders of Belgrade was built within the lower walls of the Jakšić Tower, right next to the religious complex. There was a larger ossuary next to it, where the staircase connected the church plateau with the higher section of the fortress. From 1931 to 1937, the remains of 3,529 identified, and 1,074 initially unidentified soldiers were reinterred at the Belgrade New Cemetery. After the Belgrade Zoo was opened in 1936 under the former larger ossuary, the restaurant "Kalemegdan Terrace" was opened on top of the rampart. After the war, in the late 1940s, the restaurant expanded inside the tower. The restaurant, under its original name, so as the staircase to the church, still exist. A smaller number of Dorćol's residents considered Ružica their parochial church, even though it was officially a military church. However, during World War II, the church was closed. German occupational forces took over the fortress and re-militarized it. Collaborationist administration invited priests and adherents to continue using the church, and to "keep it alive", but the residents refused. The clergy house was demolished during the massive Allied Easter bombing in April 1944. Only after World War II, with the new Communist government, Ružica stopped being military and garrison church, and worship services began to be conducted by the monastics and priests of the Patriarchate and the Eparchy of Belgrade-Karlovci. Serbian Orthodox Church set an unofficial rule that the services and sermons in the Ružica were held by the professors from the Belgrade's Saint Sava Seminary. The Ružica church is served by male priests, while the Saint Petka's chapel is served by nuns. The church, and the fortress' Kalemegdan Park, are still traditionally visited by children on Lazarus Saturday, which is among Serbs considered a children's feast. It is also known as Vrbica, cause young branches of willow (Serbian vrba, vrbica meaning "young willow") are picked, and children are given small bells. During the rigid Communist period after World War II,