St Michael's church is the only medieval church in the city centre. It stands in St Michael's Square in the Old Town which lies to the S of the main centre. It consists of a shallow aisled chancel, a central crossing with a tower, and a nave with aisles, so that the plan is effectively a rectangle half as wide as it is long. The crossing is the oldest part of the building, dating from the end of the 11thc. The original church was thus cruciform, but apart from the lower part of the tower it has all been rebuilt. In the later 13thc. chapels were added to the chancel on the N and S and their arches still remain, and at the same time the E window was replaced with a larger one whose jambs survive. In the later 14thc the E section of the N aisle was rebuilt, and the S transept was opened up to the nave aisle. The S aisle was rebuilt in the 15thc., and the tower was also rebuilt on its original lower storey in this period. The spire was added in 1732. A chantry chapel was added to the S of the S chapel in the 16thc. It is now gone but the arch to the chapel remains. In 1828-29 the nave arcade was replaced, the aisle walls raised and the N aisle lengthened westwards. VCH describes the new pillars and arches as flimsy; Pevsner prefers slender and elegant, but the aim was to allow galleries to be inserted. These were removed in 1872. As for surviving Romanesque work, we have the 11thc crossing arches, a short blind arcade on the W face of the tower, above the W crossing arch, and an important Tournai marble font of c.1170.

Southampton was a borough in the Domesday Survey, and St Michael's church was later given by Henry II to the canons of the Priory of St Denis, Southampton.

Pevsner and Lloyd suggest a date of 1066-76 for the first building campaign, corresponding to the settlement of Normans in Southampton, and the List Description agrees, suggesting c.1070. The panels in the sills of the blind arcade may come from the same period, but they are clearly reset.

The star attraction is the Tournai font. The so-called Tournai marble is a dense carboniferous limestone quarried on the banks of the river Scheldt near Tournai and either exported as freestone for decorative carving (as at Lewes Priory (Sussex)) or worked nearby and the products, mostly fonts, exported. This vigorous industry extended from the 12thc to the end of the 15thc. An English group of seven 12thc. Tournai School fonts was established by Allen and Kitchen in 1894 articles. They were: St Mary Bourne, East Meon, St Michael’s Southampton and Winchester Cathedral (all Hants), Lincoln Cathedral and Thornton Curtis (both Lincs), and St Peter’s Ipswich (Suffolk). A fragment of a Tournai font was discovered in the town ditch in Ipswich in 1894, later being moved to Ipswich museum, but it was not included by Allen in his 1903 VCH contribution, probably because it was not in Hampshire. In fact it was largely ignored until the re-examination of the material by Drake (1993). Since Allen's original paper, three other fonts have been attributed to the group: Boulge, Romsey Abbey (Hants) and Iffley (Oxon). More recent scholars, notably Drake (1993 and 2002), have cast doubt on these attributions. According to Drake, the Romsey Abbey font was said to have been destroyed c.1850 during a restoration, but there is no other evidence that it ever existed. The Iffley font is of black limestone but is uneven in shape, undecorated and unlike other fonts in the Tournai group. As for the Boulge font; Drake asserts that the finish of the bowl is too smooth for decoration to have been chiselled off it (as suggested by Eden), and points out that the bowl is too tall for its width, in comparison with genuine Tournai School products.

The presence of four Tournai fonts in Hampshire, has been linked to the patronage of Henry of Blois, Bishop of Winchester from 1129 until his death in 1171. The links to the see were very close, and he was the obvious candidate to import expensive furnishings from overseas. Pevsner (1967) dates this font c.1170, which seems rather later if the involvement of Henry of Blois is accepted. The Southampton font is unusual in showing beasts in roundels: Cahn (1977) noted only three examples, at Dendermonde (near Gent) and Winchester Cathedral as well as here, and the other two have the motif on only two of the faces. No other font in the group uses the same limited range of motifs so consistently. Most interesting is the W face, hard to see and photograph as the font is currently set up, which appears to shown three of the Evangelist symbols, missing only St Luke.