C12 reused material.
C13 tower, upper two stages rebuilt with original material in 1876, belfry added later to tower and spire shortly after.
C13 chancel rebuilt on original site, but widened to north
Early in C14 nave arcades and clerestorey rebuilt in line with widened chancel, and c.1330 north aisle rebuilt and south porch.
Chancel walls raised and reroofed in late C15, and aisles reroofed.
Nave roof early C16.
Restoration to north aisle, buttresses inscribed 'TA IP CW 1684' and '1684'.
Pebble-rubble, limestone rubble, reused mediaeval stone with dressings of Weldon, Ketton and Barnack stone.
Clerestoreys with early C16 embattled parapet has four windows with Y-tracery in two-centred arches.
Doorway c.1260 has a two-centred moulded arch carried on circular shafts with moulded capitals and bases.
Chancel has reused C13 moulded string-course decorated with mask corbels.
North and south walls of six bays with similar arches with four lancet windows, one original blocked doorway to north, windows and doorway in south wall altered in C14
Chancel arch c.1250, arch carried on single detached shafts with moulded capitals and bases.
South and north arcades c.1330 and similar, of four bays with two-centred arches, octagonal piers with moulded capitals and bases.
Roofs of both aisles of twelve bays with moulded timbers with carved figures on wall-posts of north aisle, wall posts of south aisle have carved angels.
Roof of porch C15.
Font, plain octagonal bowl with moulded soffit and octagonal stem.
TL1876 : Alconbury, St. Peter and St. Paul's Church: The font 2
C15 glass in spandrels of clerestorey windows.
Three lockers in east wall of chancel, C13.
C14 piscenae in aisles.