St. Martin Busskirch, Roman Catholic church in Busskirch, Rapperswil-Jona, Switzerland

St. Martin Busskirch is a medieval Gothic church in Rapperswil-Jona built on the remains of a Roman structure from the 1st to 4th century. The building features characteristic Gothic elements including a tall tower, pointed arches, and small colored windows that allow soft light to filter through the interior.

A first small church dedicated to Martin of Tours is thought to have been built in the 7th century on the walls of a Roman villa rustica of the later 1st century AD. A Carolingian hall church followed, then a Romanesque building around 1100, replaced around 1300; the Gothic choir, tower and saddle roof date from 1482/83. From 840 to 1838 the parish belonged to Pfäfers Abbey, becoming independent in 1838 and part of the Jona parish in 1945.

The name Busskirch derives from "Fussinchirichun", recorded in a 854 deed kept in the St. Gallen abbey archives. Until 1945 the church was the parish church of a large parish that once included Rapperswil and today's Jona; since 2008 it belongs to the merged Catholic parish of Rapperswil-Jona. The churchyard beside the building still serves as the village cemetery.

The church stands on a peninsula at the mouth of the Jona on the upper Lake Zurich, with the cemetery beside it; the site is reached on foot from Jona and Busskirch. The late-Gothic nave, polygonal choir and tower are best seen from outside, and the 1975 renovation exposed Roman wall remains in the interior. The lakeshore and the flat ground at the river delta are close by.

In 1927, workers found the remains of a Roman hypocaust, the underfloor heating of a villa rustica from the second half of the 1st century AD. Its walls had once been painted in bright colours in the Pompeian style. Three stone steps by the cemetery entrance are thought to be the access to that heating chamber.