Bolingbroke Castle

The site was first fortified by the Saxons in the 6th or 7th century, and in the 12th century the Normans raised a motte-and-bailey on a nearby hill above the settlement. The present castle was founded in 1220 by Ranulf, Earl of Chester, shortly after his return from the Fifth Crusade. It is one of the earliest examples of a uniform castle designed and built without a keep: an irregular polygonal enclosure relying instead on a curtain wall up to five metres thick, five D-shaped corner towers and a twin-towered gatehouse, the whole originally ringed by a water-filled moat 31 metres wide. Ranulf built Beeston in Cheshire on the same keepless principle in the same period, and design similarities have been noted with the contemporary castle at Boulogne-sur-Mer.

Most of it was built of local Spilsby greenstone, a porous limestone that deteriorated rapidly in the weather — a substandard material whose failings would dog the castle for the rest of its life. Ranulf died in 1232 without a male heir, and his titles, lands and castles passed to his sisters.

Following the death of Henry of Grosmont, 1st Duke of Lancaster, in 1361, Bolingbroke passed through marriage into the ownership of John of Gaunt. His wife Blanche of Lancaster, Grosmont's daughter, had herself been born at the castle in 1342. Their son Henry was born at Bolingbroke in 1367, and it was this birthplace that gave him the name he carried until 1399 — Henry Bolingbroke, the man who took the throne of England as Henry IV.

By the 15th and 16th centuries the castle had fallen into disrepair, though repairs were carried out in the Tudor period. It served the auditors of the Duchy of Lancaster, and its buildings took the names of the officials who used them — the Receiver's Tower, the Feodary's Tower. Lead for the gatehouse roof was salvaged from an abandoned chapel at Trusthorpe. The patching could not keep pace with the failing greenstone: a survey of 1636 found every one of the towers effectively beyond repair.

At the start of the First English Civil War the decayed castle was pressed back into service as a Royalist garrison. In 1643 it was badly damaged in a siege during the Battle of Winceby. The Royalists recaptured it from the Parliamentarians the following year, but defeats elsewhere forced them to relinquish it again. In 1652 the castle was slighted to prevent any further military use, its towers and walls torn down and dumped into the moat. The last major structure standing collapsed in 1815.

The ruin was excavated in the 1960s and 1970s, and much of the lower walls and the ground floors of the towers can still be traced. English Heritage maintained the site until 1995, when Heritage Lincolnshire took charge.