Castle Thorpe consists of a mount with two adjoining baileys and the remains of an apparently rectangular enclosure. The motte is now much mutilated and stands on the south side of the inner bailey which has two entrances on the W and NW. Also within this bailey stands the church. All the southern earthworks have been destroyed by village growth but some of their remains have been incorporated as garden features. Remains of a large fishpond complex survive south of the railway. (PastScape)
Today Castlethorpe Castle survives as a complicated system of earthworks which extend over an area of some 10 hectares. The motte and bailey itself, the earliest part of the works, lies immediately north-west of the church, occupying a naturally strong strategic position overlooking the valley of the River Tove. The motte lies in the southern quarter of the bailey and has the general appearance of having being disturbed or slighted at some time in the past. It survives as a substantial earthen mound, oval in plan, and with dimensions of 40m WNW by ESE and 27m transversely. Rising 4m from the interior of the bailey on the north side to a narrow summit 8m by 4m, it falls 2.1m on the south side to a platform with dimensions of 7m E to W by 5m N to S. The platform is slightly hollowed to a depth of 0.3m and could represent the foundations cut for a tower, though no surface remains now survive. This hollow may alternatively relate to a second World War gun position that is said to have been dug into the motte. The surrounding bailey is roughly circular in shape with an interior diameter of 100m. It remains well defined and intact throughout most of its extent, with the exception of SE quarter. Here the church and churchyard encroach into the site and have destroyed any surface traces of earthworks. Where the bailey defences do survive as earthworks they are of considerable strength. In the SW they utilise the natural hillside to maximum effect, the bailey scarp, possibly artificially steepened, rising to a height of 6m from the bottom of the outer ditch which is over 6m wide and 2m deep. Around the western quarter, the defences comprise a substantial ditch 18m wide and up to 3.4 m deep on its inner slope, 2.6m on its outer, This is flanked by an outer counterscarp bank up to 1.7m high. Two causewayed entrances cross the ditch in this western area; both are some 4m wide and of similar appearance, and although it is unlikely that both are original, it is impossible from surface inspection to say which is the earlier. The ditch continues around the north of the enclosure and is of similar proportions, though the outer bank ends 60m east of the northern entrance gap. Towards the eastern end of the ditch a bank 1.7m high surmounts the inner slope of the ditch running for some 50m before ending in the boundary of the churchyard. The interior of the bailey is generally flat, though with discreet surface irregularities which indicate possible building foundations, Linear undulations and shallow hollows to the north-east of the bailey represent the remains of a field system and subsidiary buildings. The considerable strength of the bailey defences in relation to the less impressive motte gives defence emphasis to the bailey. This may indicate an initial earthwork phase with a motte added at a later date. To the west of the motte and bailey castle, at a distance of some 50m, is a linear earthwork orientated NE to SW, and running for a total length of 220m. This appears to be designed as an outer defence to the main earthworks, creating a second outer bailey. The southern portion of this earthwork comprises a substantial rampart averaging 14m wide and 2.2m high, with an outer ditch along its western side 5m wide and 1.5m deep. For some 60m from its south end the east edge of the rampart has been cut back and revetted to form the western boundary of a sunken garden, The remaining northern 80m ends in a mound which has been interpreted as a barbican mound, designed to protect an entrance which passes through the outer work at this point. The outer ditch of the work continues north beyond the entrance gap, running out after some 70m. A slight bank and scarp links at right angles from this line of ditch to the outer bank of the inner bailey. If the southern end of the rampart also once linked to the inner bailey, suggested by a slight east turning at this end, then it would have formed a rectangular outer enclosure some 200m long by 60m wide. However, the modern road and railway line which cut across this area NW to SE have destroyed any earthwork surface indications which may have existed in this area. (Scheduling Report)
Destroyed by King John and rebuilt in 1292 when licence to crenellate issued 'quendam murum circa quoddam viridarium infra mansum suum de Hamslape'. King writes this licence was for a garden wall only; however it is possible to interpret the wording to mean the house. "to make a wall ... round a garden within his dwelling house ... and to crenellate the same" is the 'the same' the wall or the dwelling house? An additional issue is a garden within the dwelling house. This is interesting evidence of a medieval designed landscape.