Srednovekovnata zărkva v Ulpia Oescus pri s. Gigen, Plevensko. Opit za văzstanovka. The mediaeval church of Ulpia Oescus near the village of Gigen, Pleven district. An attempt at reconstruction - Bojadžiev, Stefan (Izvestija na Muzeite v Severozapadna Bălgarija, 17 (1991), 1991)