Hadleigh castle is a Norman fortress, construction of which began in 1230AD at the instruction of Hubert de Burgh. Hubert was a powerful baron (Justiciar of England and Earl of Kent) and had been granted the land whilst chamberlain to King John. Shortly after construction had begun, Hubert fell from royal favour, was imprisoned, and his castle seized by the crown.

Hadleigh Castle was considered strategically important, guarding the Thames estuary and the approach to London. It is therefore unsurprising that Henry chose to continue funding the castle, allowing construction work to continue unhindered. In the late 14th Century, the castle was extensively remodelled at the instruction of Edward III. The majority of the remaining ruins date from that period.

Although Hadleigh was to remain a crown castle for 200 years, it became custom for the king to grant a life tenancy to its current occupant. In later years, it became traditional for the castle to pass to the king's consort as part of her wedding dowry. In this fashion, the castle passed through the hands of three of Henry VIII's wives - Catherine of Aragon, Anne of Cleves and Catherine Parr.

In 1551, Edward VI sold the castle to Lord Riche, who proceeded to plunder the building for stone. It was allowed to fall into disuse and disrepair, and by the 17th Century, it was in a ruinous state.

Today, the most obvious surviving remains are those of the 14th Century round towers. One one still stands to its original height, but the second has suffered from landslip and is largely destroyed. Fragments of curtain wall are the only other remains of note.

Hadleigh Castle is a welcome oasis of calm on the edge of the busy urban sprawl that covers most of the local coastline. The countryside around the castle provides pleasant and unexpected relief, extending down towards the marshland that borders the sea. This has led to the area becoming an extremely popular spot for picnickers and dog walkers, and the visitor is very unlikely to find the castle deserted.

Looking out across the Thames estuary, the industrial refineries of Canvey Island line the distant horizon. This view provides a curious juxtaposition for the medieval remains of the castle, but rather than being intrusive, the dramatic and unusual vista actually enhances the haunting atmosphere of this forgotten corner of Britain's history.