Church of Mary de Castro, Leicester

St. Mary de Castro (meaning St. Mary of the Castle) is an ancient church located near Leicester Castle. Today it acts as a parish church in the Church of England's diocese of Leicester. It dates its founding to 1107 when Henry I of England took the lands and castle from a rebellious owner and granted them instead to Robert de Beaumont, although some legends say that a Saxon church of St. Mary had existed before the Norman Conquest. The collegiate nature of the church lasted until the college was disbanded in 1548 by Henry VIII.

The early-12th-century church had no aisles, and various parts of these walls survive. It underwent a major expansion in the 1160, with a north aisle, doorways to north and west, and an extension to the chancel. The two doorways provide striking external Norman zigzag decoration, but it is the Sedilia and Piscina in the Chancel extension that Pevsner describes as "the finest piece of Norman decoration in the county". Thirteenth-century alterations culminated in a major reworking of transepts and south aisle, to create an aisle wider than the nave, providing much more space for local parishioners. Also the huge east window of the south aisle, with ingenious tracery, was created around 1300.

The tower was built inside the south aisle, apparently as an afterthought, rising to a quatrefoil frieze, four decorated pinnacles, and the needlelike spire rising from the battlements. The spire was completely rebuilt in 1783, but retained its crockets and three tiers of lucarnes. The interior was worked on by George Gilbert Scott throughout the 1860s.

The church was closed when the spire was found to be unsafe. The 14th-century octagonal spire, having been rebuilt in 1783, had developed six-metre-long cracks in four of its faces in September 2013. After inspections by structural engineers, it was deemed at risk of collapse. The severe condition of the spire meant it had to be demolished, at an estimated cost of £200,000, in 2014. Over £358,000 has been raised since 2011; however, there are currently insufficient funds to rebuild the spire and repair the tower.

The church contains a three manual pipe organ which was originally installed in 1860 by Forster and Andrews. It has been the subject of modifications and restorations in 1880 by Joshua Porritt, and R. J. Winn in 1960. A specification of the organ can be found on the National Pipe Organ Register.