The decoration of the elongated north and south walls include brick blind arches in the bottom part and a large arch for each wall adjacent to the dome with a columned window in the middle . There are windows above the lower arches of the north and south facade . The dome , which also exhibit a large number of ornamental details and ceramics , feature eight windows , one for each of its sides . The medieval frescoes which was painted on the interior walls of the church have been only fragmentarily preserved .