The local legend goes like this: some time ago a child was strangled by his stepmother and thrown into the Miljacka river. Local people who knew of the tragedy told the priest of this church, and he took the child from the river and buried the body behind the church.
After some 100 or 200 years, the body was exhumed because the Church wanted to build on the grounds. When they saw that the child was well preserved, it was declared a miracle and the body was taken inside the church.
Pregnant women and mothers who wish to symbolically protect their children pay homage to the body of the young boy preserved in the old Orthodox church of St. Michael the Archangel, in Sarajevo. The child’s mummified body is positioned on an upper floor tomb on a trestle structure, so that one can pass beneath the child’s body and be blessed by it.
To this day, women “who wish to encourage their fertility or to protect their children” walk around the structure three times and then crawl under it.
Source: AtlasObscura.com