The bell-shaped crocket capital of a pilaster in the south nave of the monastery church, demolished in 1945, is ornamented with stylised foliage (palmettes along the upper edge, flowering rosebuds in the central part, intertwined stems in the lower part). 

The Fons Beatae Mariae Virginis monastery in Kostanjevica was founded by Bernhard von Spanheim. He issued the first foundation charter, which has not been preserved in either original form or as a transcript, in 1234, while the second, more complete charter dates from 8 May 1249 (kept at the Archives of the Republic of Slovenia); with the latter, the monastery became a dependant priory of the mother house monastery in Vetrinje (Viktring). 

The Kostanjevica monastery church has a Latin cross floor plan (the so-called “Bernardine layout”), based on the bound system typical of Romanesque construction, with a rectangular choir, a transept and two pairs of chapels with square termination. In addition to the vaulting system, the church is distinguished by the ornamental stonework on the capitals of the pilasters and compound pier shafts; Emilijan Cevc found many similarities with the Cistercian Abbey Church in Bélapátfalva in Hungary (founded in 1232).