EN
The Chapel of St. Margaret of Antioch in Kopčany in western Slovakia is dated to the period from the 2nd half of the 9th century to the 1st half of the 10th century. The radiocarbon analysis of the wood residues from the cavity in masonry dates the building to the year 951 ± 60 (i.e. 891 – 1011). The completely preserved intact primary pre-Romanesque window openings were discovered in the north wall of the chapel. A specific feature of these window openings is the vaulting with the triangular keystone. The paper takes a closer look at this architectural element. The triangular keystone is to be regarded as a cultural import from the pre-Romanesque Carolingian architecture or from the area of its later occurrence in the West European early-Romanesque architecture, where it was used in the representative, especially sacral buildings as a structural detail with a decorative function and a special symbolic content.