Saltwood Castle is in Saltwood village, one mile north of Hythe, Kent, England. The castle was probably erected on a Roman site, though Bronze Age implements and copper ingots discovered in Hayne's Wood, 1874, show the site had already long been inhabited.

The castle's site traces its history back to 488 CE, when Aesc, the son of Hengist and the King of Kent, built a castle on the site. It first appears, however, on a charter of King Egbert in 833. The manor of Saltwood was granted to the priory of Christ Church in Canterbury by a deed dated 1026. Under William of Normandy, Saltwood, held by the Archbishop of Canterbury and let, under knights’ service, to Hugo de Montfort, formed part of the string of large fiefs granted from Hithe to the New Forest, along the south coast of England. The structure was replaced by a twelfth-century Norman structure, with work extending over the next two centuries. It became the residence for a time of Henry of Essex, constable of England.

Thomas Becket had asked Henry II on behalf of the Church for the restoration of the castle as an ecclesiastical palace. Henry instead gave it to one of his loyal barons named Ranulf de Broc. This leads to the implication that some complicity was possible in the murder of Becket by the baron Ranulf de Broc. It was during this time at Saltwood, on December 28, 1170, that four knights are presumed to have plotted the death of Becket, which took place the following day at Canterbury Cathedral, about 15 miles away. Hugh de Moreville was one of the four knights that committed the assassination, along with Reginald Fitzurse, William de Tracey, and Richard le Breton.

After Becket's assassination, the castle was returned to the control of the archbishop of Canterbury. Saltwood remained a church property until the reign of Henry VIII when Hythe and Saltwood were seized by the Crown. It became uninhabitable as the result of the earthquake of April 6, 1580, but was restored in the nineteenth century, as a residence once again of the Archbishop of Canterbury. The gatehouse has been used as a residence ever since.