[1] The building fulfilled its manor house function for most of its life, never withstanding an armed attack or siege but becoming one of the chief episcopal strongholds and an agricultural focus for the Bishop’s estates in Sleaford and elsewhere.

An outline of a 40 by 15 metre tithe barn (said to be the largest in England, and with a cattle shed and hay loft attached) can still be seen in the southern half of the castle.

John Leland described it at this time as well maintained with a gatehouse, which housed two portcullises, and a high central tower, "but not sette upon a hille of raised yerth".

[6] The castle began to fall into disrepair during the second half of the 16th century with the timber and lead roof being removed to be reused in buildings in the town, some of which survives to the present day.

[8] The castle was excavated to determine its layout, and the finds included a floor tile fragment which featured a cat paw print on it, and also a Jetton of Hans Krauwinkel II from Nuremberg, dated to 1586-1635.