The adoption of Christianity by the Slavic tribes inhabiting the valleys of the Warta, Odra and Vistula initiated a turn in the field of culture and art. Before baptism, there were monumental fortifications and residential architecture, as well as religious temples, which remain unknown. By the mid-10th century, the first religious buildings made of stone appeared in Poland. The adoption of Christianity initiated a specific symbiosis of huge fortifications made of wood and earth and stone buildings with a long tradition dating back to late antiquity and early Christianity. After World War II, archaeological excavations revealed the relics of many early medieval stone buildings. Among them there is a group of buildings traditionally associated with the 10th century or the beginning of the 11th century. In Greater Poland, this group includes: the first cathedral in Poznań, the oldest relics under the cathedral in Gniezno, the first monastery church in Trzemeszno and palace complexes in Ostrów Lednicki and Giecz. Małopolska has a large group of buildings on Wawel Castle and the rotunda of St. Benedykt in Krzemionki. The discoveries in Przemyśl and Wiślica are also extremely important, palace complexes were also found there. The criteria for the early dating of the discussed group include: archaeological stratigraphy, material and technique of wall construction, as well as the arrangement of forms presented by individual buildings. They were made either of cut stone, here and there using the "opus spicatum" technique, or of elements of slate, typical of Małopolska. Dating individual buildings from this group is difficult, mainly due to the paucity of written records and the complete lack of contemporary written information about the foundation, construction or consecration of a given temple. Existing sources come from later periods and are often misleading. If the year 1000 were a strict cut-off point in the field of stone architecture, we could only deal with the Poznań cathedral and a few relics from Gniezno, because the remaining monuments could not be precisely dated. Following the typological order, the Poznań cathedral is mentioned as the first building. It is generally considered to be the first monument of Piast architecture, especially now that the research and documentation work has been completed, and the interpretation carried out by Krystyna Józefowicz is beyond doubt. The identification of this building as the oldest cathedral in Poznań and the dating of its construction to the years immediately after the ordination of Bishop Jordan have not been questioned so far. It is worth emphasizing that the first religious building known to us took a monumental form. Another group of early medieval buildings are the relics found under the Gniezno cathedral. The problems associated with them are more complex than in the case of the Poznań cathedral. Previous publications do not include a list of drawings and descriptions of the relics. Nevertheless, the finds allow us to assume the existence of two of the oldest buildings, one Romanesque and the other pre-Romanesque. There are some fragments of the building older than the two basilicas - due to their fragmentary nature they cannot be interpreted more precisely. Many archaeologists date this pre-Romanesque basilica to the period before 1000. Historical considerations also support such a date.