The Benedictine Abbey in Tyniec is the oldest existing monastery in Poland (11th cent. AD). The historic walls of the Monastery have survived to this day and crown the limestone hill on the Vistula River. The geological structure of the surrounding area is reflected in the composition of the mortars.

In vicinity of Tyniec one may observe outcrops of Upper Jurassic limestones represented by two facies: bedded limestones with cherts and massive limestones. Recently, it was discovered that the monks not only fortified the Tyniec hill but also partly built it up with loess. Additionally, a massive “stepped” stone platform was later built to strengthen the edge of the hill. The mortars radiocarbon dating provides the first attempt to obtain the wide chronology of the extension of Tyniec. For this purpose, the chronologically oldest layers were analyzed.

Sequential dissolution of mortars was applied to separate the carbonates of different origin. The obtained results illustrated the huge influence of mortar components and the local geological structure on the 14C measurements. In addition to the mortar, 14C measurements were also made for charcoal from Tyniec Abbey. Radiocarbon dating was performed on the selected fractions using accelerator mass spectrometry (AMS). Radiocarbon dating results of samples from the oldest part of the stone platform make it possible to associate its construction with the earliest monastery buildings.