What is "kulb"

Kulb is a village on the Nile in northern Sudan. It has been inhabited since the time of the Christian kingdom of Makuria. Until the 15th century, it was in a remote area, serving as a retreat for Christians in Nubia. The domed Kulubnarti church, located on Kulubnarti (Kulb Island), is the only known example of a Christian center plan building in Lower Nubia.