San Sebastiano is an Early Renaissance church in Mantua, northern Italy.
Begun in 1460 according to the designs of Leon Battista Alberti, it was left partially completed in the mid-1470s, by which time construction had slowed and was no longer being directed by Alberti. As a consequence, little remains of Alberti’s work apart from the plan, which is considered one of the earliest and most significant examples of Renassiances centrally-planned churches. The plan is in the shape of a Greek cross, with three identical arms centering apses, under a central cross-vaulted space without any interior partitions. The church sits on a ground-level crypt which was intended to serve as a mausoleum for the Gonzaga family.
The complete absence of columns in the façade signified for Rudolf Wittkower a decisive turning-point in Alberti's interpretation of architecture, moving beyond his statements in De Re Aedificatoria where he considered the column the noblest ornament of building.