ENDuring the almost 20 years long archaeological investigation of the territory of Vilnius Lower castle (1987— 2006), more than earthenware 5000 floor tiles were uncovered. They can be classified into more than 40 types according to the form, glaze and decoration. The present article describes the embossed floor tiles uncover in the layers of the second half of the 15th—the beginning of the 16th centuries decorated with mystic creatures and scenes illustrating Bible narrations. Most of the tiles are rhomb-shaped. Their surface is covered with green glaze, threadbare, sometimes charred and porous. The sides of the tiles are slightly bevelled. The tiles have impressed rectangle frames in their centre (not contained in the rhomb form) with shallow raised ornaments. The dimensions of the tiles are: the rhomb axes ~ 16.5 - 17 x 26.5 cm, side lengths ~ 14.8 - 16.5 cm and the thickness ~ 1.8 - 4.0 cm. The plots of decorations are of two types: 1) the whale engorging Prophet John (fragments of 15 such tiles were uncovered) and 2) a pair of dragons with entwined necks and long ringed tails (13 fragments). There is a hardly visible Gothic inscription in the upper part of the tiles with John. This scene was often depicted in the manuscripts of the 14th—15th centuries. One of such manuscripts stored at the Vienna National Library contains a picture with an inscription above JONAS IN MARE PICEBAT. Presumably similar inscriptions are contained in the tiles from the Vilnius Lower Castle. The square and rectangular tiles are decorated with images of lions, mermaids and other mystic creatures. Most of the images are fragmentary therefore the entire design so far cannot be reconstructed. The dimensions of the tiles are: from 10x?cm, 15- 16x14.5 cm; thickness - 1.5-3.5 cm.The sides are right-angles or bevelled. The surface is covered with green glaze. The tiles with mermaids are of two types. One of the image types depicts a mermaid amid palm leaves. The other type of images is represented by mermaid Meluzina with two tails. Both types of the tiles with mermaids have a common feature, i.e. fish image at the bottom. Many researchers seek for the roots of the legend about a mermaid with two tails in the Celtic mythology yet the stories about zoomorphous water creatures (mermaids) have been characteristic of the folklore of many nations. In the European Medieval legends, mermaids were poised between the good and the evil and had the powers of fairies and daemon. The greater part of the tiles uncovered in the territory of the Vilnius Lower Castle is concentrated around the early brick buildings. Some of brick buildings were built in a wet ground and have timber poles in the basement constructions. Dendrochronological investigations showed that the stone works were built at different times: some of them the first half of the 14th century the other in the second half of the 15th century. Buildings M 2 and M 3, whose interiors might have been decorated with floor tiles, have no timber poles.Architect Dr. N. Kitkauskas dates the buildings to the second half of the 13th century according to the tile binding technique. No archaeological layers linking these buildings with the 13th century were found. Only solitary stray finds were uncovered which based on analogues could be dated to the end of the 13th-beginning of the 14th centuries. The early brick buildings were demolished when building the Royal Palace and expanding its courtyard. At the beginning of the 16th century, almost all early layers were removed. Only small pits for domestic waste containing the rugged earthenware from the 5th-8th centuries and scanty fragments of the layer dated to the 14th— 15th centuries in the western part of the courtyard have survived. The floor tiles were uncovered together with the fragments of Gothic tiles in the layers dated to the end of the 15th— the beginning of the 16th centuries and could have decorated the interiors of the buildings in the middle and the second half of the 15th century before demolition. The closest analogues of the floor tiles and Gothic tiles uncovered in the Vilnius Lower Castle are known in Poland, Czechia and Hungary. At certain time intervals of the end of the 14th and in the 15th century, these states were related by common sovereigns and dynasties. In the reign of Kazimieras, the all four Central European monarchies belonged to Jogelonians.