The Cromwell Museum is situated in the medieval centre of the town, immediately E of All Saints parish church. It was formerly the Grammar School attended by Oliver Cromwell and houses a display dedicated to him, but was built as the infirmary hall of the Hospital of St John the Baptist.

In its present state it is simply a rectangular box with a pitched roof and gabled ends at E and W, but it was originally longer and aisled. What remains are the two W bays without their aisles. The arcade piers and arches remain, but the bays have been blocked and triplet windows inserted in the arches. At the E end a plain gabled wall has been built to close off the structure, and a simple pointed doorway and a three-light window in a late-14thc style inserted. The doorway is a reused medieval piece, probably 13thc, but the window is entirely 19thc. The W facade is the glory of the building, with an elaborate off-centre 12thc doorway with rich chevron decoration, a chevron-decorated lower window, and at higher levels arcading that frames the two upper windows and a single oculus in the gable.

Much of what we see results from a restoration in 1878, when it was completely rebuilt, and the 19thc brickwork used to raise it by 3 feet is visible at ground level. Much of the original sculpture was reused, including most of the decorated W doorway and window, parts of the W facade arcading, and the bases and capitals of the arcades.

It is clear from the E pier of the S arcade that the building originally extended further E. Pevsner states that it was seven bays long, and that there was a courtyard to the N around which the Master’s lodging, the refectory and other buildings were arranged.

The Hospital of St John was said to have been founded by David, Earl of Huntingdon. This gives two possible candidates, both members of the Scottish royal family of Canmore. The first, who later became King David I of Scotland (1083x85 – 1153) became Earl when he married Matilda de Senlis, the daughter of Waltheof, Earl of Northumberland in 1113, and took the throne of Scotland in 1124 when his brother Alexander died. The second candidate was his grandson, David (1152-1219), youngest son of Earl Henry of Northumberland and Countess Ada de Warenne, who acceded to the earldom in 1185. His elder brother, William the Lion, had been stripped of the earldom of Huntingdon after his ill-judged support for the rebellion of Henry II’s sons in 1173-74; the title reverting to the Senlis family that had originally been awarded it by William the Conqueror. The Senlis earl, Simon III, died in 1184 without heirs, and the title was formally regranted to William, who immediately passed it on to his brother David. It seems certain that between the years 1173 and 1184 the possession of the earldom was disputed.

Of these two, the second is the likelier candidate for patron of the hospital, despite Carruthers’s description of the founder as “afterwards King of Scotland”. King David’s concerns and his power base were always further north, and although he was a noted monastic patron his activities in this area were in Scotland and not England; he founded Selkirk Abbey (1113), Melrose (1137) and a dozen other houses there. His grandson, on the other hand, was apparently based at Huntingdon and may be expected to have expended his patronage within the earldom. Further, Lansdowne 921, f.55 describes the founder as the father of Isabel de Bruce, which fits the younger David. This is not certain, however; the younger David’s biographer Stringer points out that he is not known to have founded any other religious house in England.

Pevsner dates the building to c.1170-90, placing the S arcade before the N in date.

The decoration of the W facade is one of the highlights of the mature Romanesque in Huntingdonshire; the advanced chevron and scallop forms pointing to a date in the 1160s or ‘70s. The S arcade belongs to the same campaign, but the N is later, perhaps 1180-1200 or a few years later, to judge from its capitals (especially the moulded E capital) and its water-holding bases. The belated addition of a N aisle could explain the asymmetrical appearance of the W facade: with only a S aisle the doorway would be closer to the centre of the composition. It is tempting to see the break in construction as a reflection of the disputed earldom of Huntingdon in the years between 1174 and 1184, but this kind of historical causation is seldom justified, and it would be safer to assume that David (the grandson) was named as the builder since he had completed the work, and to leave open the question of who began it. It should be noted that older secondary sources, including VCH, give David’s birth-date as c.1144.