Having established the first archbishopric (968) near the ducal palatium and the rotunda founded in 965 on the island of Ostrów Tumski, Mieszko I built a pre-Romanesque three-aisled basilica. The shrine was damaged in the years 1038-39 and rebuilt in the following years (until 1058) in the Romanesque style. In the 13th c. an early Gothic presbytery was erected and in the mid-fourteenth century a new Gothic nave was built. The reconstruction of the church in the Gothic style continued in the 14th and 15th century, during which a new presbytery with a chevet and a row of chapels was added. In the 17th c. the church was extensively rebuilt in the Baroque style (most probably by Krzysztof Bonadura the Old, and later in accordance with a design by Pompeo and Antoni Ferrari). The church was damaged in a fire in 1772 and given a Baroque interior that survived until 1945. The façade was rebuilt in 1779 (to a design by Efraim Schroeger) and the old cupolas were replaced in 1790 (designed by Bonawentura Solari). The cathedral was badly damaged during the battle of Poznań in 1945. Reconstruction work was carried out in the years 1948-56 to a design by Franciszek Morawski who restored the Gothic form of the shrine from the 14th and 15th c. and the original appearance of the cupola from the years 1725-29.
The main entrance to the cathedra is in the front façade through the Gothic portals from the 15th c. and a bronze door (a design by Kazimierz Bieńkowski, 1979) decorated with the scenes from the life of St. Peter and St. Paul. A high Gothic window with a rosette above the portals surmounted by crow-stepped gables and blind windows; Romanesque face of a stone wall in the lower part of the south tower. It is a basilica with a chevet and two aisles adjoined by 12 chapels, 2 sacristies and a narthex. The presbytery and the ambulatory are covered with a groin vault, whereas the nave and the aisles are covered with a stellar vault.
Artefacts from Lower Silesia in the presbytery. A Late Gothic altarpiece in the middle - poliptych from 1512 with the sculptures of Mary with the Infant, St. Barbara and St. Catherine in the centre; outer wings with four panels featuring sculptures of 12 saintly women, painted scenes of the Passion and saints on the opposite side. Late Gothic stalls from the 16th c., a Flemish tapestry from the 17th c., five Late Gothic sculptures from the 18th c., a Late Gothic pulpit and a baptismal font from 1720 in the presbytery, an altar from 1971 designed by Józef Stasiński and decorated with bas-reliefs depicting the twelve apostles in the front.
The bronze plate in the floor in front of the presbytery commemorates the first bishop Jordan and 7 rulers buried in the cathedral. The nave ends in an organ loft under which there are sixteenth-century tombstones of Jan Przecławski, Janusz Przecławski and his wife Anna from Sady and Piotr Przecławski's epitaph.
There are many valuable artworks in the aisles, along the ambulatory and in the chapels, most of which are in the Baroque style. The aisles feature Teodoryk Pradel's Gothic tombstone (d. 1383), 5 Gothic and Renaissance tombstones from the 14th and 15th from the Vischer's workshop in Munich (stolen by the Germans during the war and returned by the Russians in 1990), a tomb of Bishop Benedykt Izdbieński, a work by Polish Renaissance sculptor Jan Michałowicz of Urzędów. The chapels boast an impressive Renaissance tomb of the Górka family from 1574 (the Chapel of the Holy Sacrament), and St. Martin's Entry to Amiens, a painting by Krzysztof Boguszewski from 1628 (St. Martin's Chapel).
Two chapels are of special prominence: the Golden Chapel (the Chapel of Polish Sovereigns) and St. Stanislaus's Chapel, also called the Royal Chapel. The first is modelled on Byzantine architecture and features a tomb from 1840 with the mortal remains of Mieszko I and Bolesław the Brave and a monument to both rulers, the work of Christian Rauch from 1841. The Royal Chapel could once boast the tomb of King Przemysł II but presently it features an impressive epitaph honouring the sovereign (a work by Marian Konieczny from 1995). In the vaults there are remains of the Early Romanesque and Romanesque cathedrals discovered in the years 1946 and 1951-56 and the alleged graves of Mieszko I and Bolesław the Brave. Below the west part of the presbytery there is a collection of stone tombstones and epitaphs and the burial vault of local archbishops and suffragans built in 1963.