Ostrow Tumski, the only island on the Warta River in Poznan, is the oldest part of the city. The origins of Poznan and the state of Poland are closely associated with this site. It is here that the first pre-Piast stronghold was established in the 8th or 9th centuries. The first Piast settlement appeared a century later. Originally, the city was located on the right bank of the Warta River. According to the recent archaeological research, in the western part of Ostrow Tumski there was a ducal palace built in the first half of the 10th century. At that time it was the largest two-level brick lay structure of the Piast state. It was the largest settlement and with the largest fortifications of the Piast dynasty. The golden age of the site did not last long. A century later the flood, the invasion of Brzetislav I, the Bohemian king and pagan reaction destroyed the settlement. Kasimir the Restorer rebuilt and expanded the city, but Poznan was no longer a capital city. In the 13th century Przemysl I moved the city and the ducal (then royal) seat to the left bank of the Warta River. Ostrow Tumski became under the rule of the bishops of Poznan.
Ostrow Tumski is not only known as the oldest part of Poznan. It is also one of the most interesting complexes of Gothic and Baroque architecture in Poland. This ''sacred city'', situated in the forks of the Warta and Cybina Rivers, abounds in historical sights of which the most important ones include the Cathedral, the Church of Our Lady in Summo, the Psaltery and the Lubranski Academy.
The Archdiocese Basilica of St. Peter and Paul, also referred to as the Cathedral, is the oldest cathedral of Poland. Its origins date back to 968 , two years after Poland adopted Christianity, when the first Polish bishoprics was established in Poznan. Originally, it was a pre-Romanesque basilica, erected on the site of two baptisteries, built by Mieszko I. It is here that the oldest necropolis in Poland, where the first rulers of the Polish state: Mieszko I and Boleslaw the Brave were interred, is situated. Over the centuries the church has been rebuilt and renovated a few times. Nowadays the basilica is an imposing building (24.5 metres high, 81 metres long and 43.5 metres wide). The brick-red twin spires, one of the most characteristic features of the temple, are 62 metres high, whereas the small spires above the ambulatory tower for 44 metres. Inside the three-nave basilica there is an ambulatory, two sacristies and twelve chapels.
To the west of the Cathedral there are two historical buildings worth having a glance at. Those are: the Psaltery and the Church of Our Lady in Summo with the ''in summo'' meaning ''on the stronghold''. This Gothic church was probably built on the site of the stronghold's chapel erected here by Mieszko I's wife, Dobrawa. The Church of Our Lady in Summo is a typical example of late Gothic of West Pomerania. The peculiarity of the site, apart from the church's interesting interior, is the bouldered stone in the plinth with secret grooves. Legend has it the grooves are the scratches made by swords while sharpening them. The stone was believed to have given them supernatural power.
The Psaltery, dating back to 1518, is a unique example of late-Gothic architecture. Jan Lubranski, the Poznan bishop, commissioned building it for the needs of the Poznan Cathedral Choir established six years earlier. The 12 psalmodists sang the psalms from the King David's Book of Pslams every two hours in the nearby cathedral. Nowadays the Psaltery is a unique monument of the musical culture of Poznan. However, the architectural details of the building are also of note, especially the most distinctive feature, i.e. the gabled top with recesses resembling the shape of a donkey's back. Though destroyed during World War II, the Psaltery was renovated in 1947.
Lubranski Academy, founded in 1518 by the Poznan bishop Jan Lubranski, is mostly renowned as the first higher education institution in Poznan. It is also regarded as the first Polish humanities-oriented educational institution. The building itself, with its facade void of rich ornamentation, is not of particularly distinctive artistic value.
The golden age for the Lubranski Academy was the 16th century when Krzysztof Hegendorfer, prominent Renaissance German humanist, gave his lectures here. Among its most famous graduates one can mention: Jan Sniadecki, famous mathematician, astronomer and university professor in Cracow and Vilnius, and Klemens Janicki, renowned poet. In 1780 the Lubranski Academy merged with the Great Poland Academy (formerly Jesuit College). Nowadays, the building houses the Archdiocese Archives.