Archaeological Sanctuary is one of departments of the Museum of the first Piasts. The sanctuary possesses a permanent exhibition presenting history of stronghold and castellany in Giecz titled “Giecz in Monarchy of the Piasts”. It is supposed that there was a pile bridge (6 meters wide and 150 meters long) over the Moskawa River and swamps, which led to the stronghold. Inside the banks of wood and soil with two towers, there are palladium foundations of stone, pieces of church and rotunda in preroman and roman style from Xth century. In undergrounds of the church a crypt of reliquary has been discovered. In that time it was a place where relics of John the Baptist were kept. Uncovered foundations of roman buildings and remains of metallurgical furnaces confirm that Giecz was an important centre of craft and trade.