The church was almost rebuilt 1340-52 to serve as the chapel for Peterhouse college, and it was attached to the college by a gallery stair.
There was apparently an intention to have a western transverse ante-chapel in the manner of Merton College, Oxford, but this was never built, and the westernmost bay adjoining the tower was completed or rebuilt in the C15.
Other work in the C15 included new tracery in the side windows, at least on the N,
possibly the reroofing of the whole building, as a scar of a low-pitched roof is visible at the W end, although the roof was also redone in the C17.
A chantry chapel was added on the N in 1443 for Thomas Lane, Master of Peterhouse
the S porch was added in the mid C15 by John Leedes, d. 1455, bursar of Peterhouse
the vestry was rebuilt and partially converted to a chantry chapel for John Warkworth c.1487
and a chantry was added on the S side in the early C16 for Henry Horneby, another Master of Peterhouse.
It is largely mid C14 in appearance
The very large E window is C14 and has six lights with excellent flowing tracery.
It is surrounded by three C15 statue niches, those on the sides with vaulted canopies, that below with a projecting pedestal on an attached shaft.
There are four C14 windows in the N wall all of four cinquefoiled lights, restored in the C19, which almost fill the bays between the buttresses.
The westernmost window in the N is C15
with the tracery restored in a C14 style.
The westernmost window on the S is C15, and the W wall has a three light C15 window with vertical tracery.
The S vestry is C14 in origin
was rebuilt in the late C15 and has two C15 E windows and one in the S wall.
There are two small openings in the E wall to let light into the ossuary below the vestry, an unusual fixture relating to medieval burial practice.
A fragment of Anglo-Saxon interlace ornament is built into the S wall of the parish room.
There is a blocked door and C15 tomb recess in the N wall for Lane chapel,
the former Horneby chapel, now the ante-chamber to the S chapel, has an early C16 door and contemporary arch for a tomb recess with an elaborate ogee frame.
The ossuary below the vestry has a C14 brick vault with clunch ribs and a central, octagonal pier.
The C12 tower arch is of two, plain round-headed orders and has quirked and chamfered imposts.
To the NE is a half arch that awkwardly joins the tower to the C15 N wall.
PRINCIPAL FIXTURES: The four-bay piscina and sedilia composition formed by carrying down the mullions of the 1st window on the S side is C14.
There is a simpler C14 piscina in the S vestry.
There are Hanoverian Royal arms, probably part of the 1741 refitting.
The stem of the pulpit of 1741 is the sole survivor of a complete C18 refurnishing of the church.
The hexagonal pulpit, with a matching hexagonal sounding board, and enriched panels in each face, one with an IHS monogram, was rebuilt in 1900.
What is apparently the former C19 reredos with rich carving, including figures of saints, is hung on the W wall of the church.
There is some good C19 glass, including the W window of 1886 by Kempe.
Stained glass in Emmanuel United Reformed Church on Trumpington Street, probably installed by Morris & Co in 1906. One of a series in the apsidal sanctuary of the church depicting Cambridge Puritans. Barrow (or Barrowe), of Clare College, was a separatist divine who was martyred in 1593, together with his colleague John Greenwood of Corpus Christi, for allegedly "devising and circulating seditious books". https://en.wikipedia.org/wiki/Henry_Barrowe
In 1286 it was transferred to the new foundation of Peterhouse
was used as the college chapel until 1632, although it retained parochial functions also.
By 1340 the church was said to be 'old and ruinous' and the scholars were not using it.
By 1352, however, the new church was sufficiently complete to be consecrated, when it was rededicated to St Mary, distinguished from the other St Mary's as St Mary the Less.
The church always retained its parochial functions, and in 1632, when a chapel was built within Peterhouse, it reverted to purely parochial use.
It was refitted in the Georgian style with panelling, box pews, a choir gallery and a central pulpit in 1741, but all of this except the pulpit was removed when the church was restored in a Gothic style in 1856-7 by Sir George Gilbert Scott, one of the most important church restorers of the mid C19.
SOURCES Victoria County History, Cambridge III , 123-32 RCHME City of Cambridge II , 280-3 Pevsner, N., Buildings of England: Cambridgeshire , 226-7 REASONS FOR DESIGNATION The Church of St Mary the Less, Cambridge is designated at Grade II* for the following principal reasons: * Interesting church of c.1340-52, built to serve as the chapel for Peterhouse with a fine E window and a gallery linking it to the college. * Unusual C14 ossuary. * Noteworthy C14 font with a C17 cover. * Restored in the C19 by Sir George Gilbert Scott. * Very strong group value with other neighbouring buildings on Trumpington Street, in particular Peterhouse.