The first permanent settlements in the area of today’s hillfort, called Grodziszczko, were built at the turn of the eighth and ninth centuries. During this period, the area was a peninsula surrounded on three sides by the waters of the now defunct lake. Around 865, it was replaced by a small hillfort located in the northern part of today’s settlement. In the 10th century, there was already a settlement complex, including a hillfort and several villages, located at the crossroads of trade routes. At the end of the twenties of the tenth century, Giecz, unlike other important Wielkopolska towns like Poznań and Gniezno, was not burned and built from scratch, but only considerably enlarged. This unusual fact served the purpose of drawing the theory that it constituted a center from where the Piasts mastered the remaining towns of the Polans. As a result of the aforementioned reconstruction, the ramparts of the oldest part of the settlement were strengthened by widening and paving with stones, while from the south they were surrounded by an earth-wooden ramparts. In this way, a two-part fortress with a clearly separated part of the prince was created.
In the eighties of the tenth century, a stone palace complex with a rotunda chapel was built inside the hillfort. For unknown reasons, the construction was discontinued after laying the stone foundations.
At the beginning of the 11th century, in the northern part of the hillfort, a stone church of St. John the Baptist was built, with unparalleled architecture in Polish lands. It was a single-nave temple, 20 meters long and 11 meters wide, with a semicircular apse. An interesting element of the building was the underground crypt of the reliquary of the unknown saint, located under the chancel. Later, the so-called westwork, that is two towers and a square inter-tower room, was added to the temple.
In 1038, the castle was destroyed during the invasion of Czech prince Bretislav I. The population was abducted and settled in the Czech. In the second half of the 11th century, the castle was rebuilt and enlarged, however, another destruction brought Giecz in the first half of the 13th century – a war between Władysław Odonic and Henry the Bearded. Nevertheless, the hillfort still enjoyed great importance as evidenced by the congress of the Wielkopolska dukes, which took place here in 1253. Only in the next century was the slow decline of the hillfort’s significance. It was most likely related to a change in the course of trade routes and the emergence of new urban centers in the area. Most probably, at the end of the 13th century, the rampart separating the northern and southern part of the hillfort was pulled down, making Giecz a one-yard complex. Probably at the beginning of the 14th century, perhaps due to the Teutonic invasion, the hillfort was deserted.
Today in Giecz, one of the central hillforts of early medieval Poland, an archaeological reserve is established. Its most important elements are: fortified settlement with an area of approx. 3,6 ha with earth ramparts having a base of approx. 30 meters and reaching up to 9 meters in height and foundations of a palatium. In the former outer bailey, it is worth seeing the fully preserved romanesque church of the Assumption of the Blessed Virgin Mary and St. Nicholas. In the museum you can visit an exhibition presenting the history of the city and castellany of Giecz, as well as the most important archaeological monuments excavated during archaeological research in the city and neighboring sites. In 2011, an educational settlement was also opened. Ticket prices and opening hours can be checked on the official website of the museum here.