The nave, north aisle and lower part of the tower, all of which date from the first half of the 13th century, and the south porch, which is Early English. In the 14th century the chancel and chancel arch were rebuilt and most of the windows in the building were replaced, all in a Decorated Gothic style. The upper part of the bell tower was added in the 15th century and the clerestory was added to the nave in the 16th century, each in a Perpendicular Gothic style.The tower has a ring of six bells. Edward Hemins of Bicester cast the third, fourth and fifth bells in 1732 and the tenor bell in 1739. Abel Rudhall of Gloucester cast the second bell in 1749 and Mears & Stainbank of the Whitechapel Bell Foundry cast the present treble bell in 1923. St. Mary’s also has a Sanctus bell that Thomas Rudhall cast in 1778.