To the south-east side of Horley there is an area of about 680 acres stretching from a point north-east of Langshott Manor to the Gatwick link road, and a point about a quarter mile east of Balcombe Road across the M23 motorway. This area was known for many years as the Manor of Haroldslea. From early times it was a detached part of the Parish of Horne, until 1894 when it was transferred to Horley. Within this area there is an unusual moat. Basically it is two concentric moats. Within the inner moat there is a main central island and a smaller island.
The site is a listed “National Monument” therefore it is not possible to excavate the site. Back in 1936 a small hole was dug and revealed that iron had been smelted there and pottery dated from around the 13th to 15th centuries was also found. Such pottery fragments are fairly common in the surrounding area.
What is known is that there was a manor court held in Haroldslea in the early 13th century. Documents in the British Library (ADD Charters 5932 & 7599) refer to the people of Horne having to pay their rents into the court of “Herewoldeslea”
There are no known old legal references to a castle in the area, indeed the first reference to Thunderfield Castle was an 18th century historian (Aubrey) who named the moat as Thunderfield Castle. During the same period several maps refer to Horne Castle. Later maps followed the tradition that the site was of Thunderfield Castle.
In view of the fact that there is no legal reference known of a castle in the area, but that there is evidence of a manor court, we are left to suggest that the site was of a timber framed manor house.
Whether or not there was ever any kind of fortification on the site is pure speculation, as nothing has ever been found, except some burnt timbers in the moat which could have come from a house or barn.
So what was Thunderfield?
Thunderfield was a common or heath which covered most of what is now Horley from Horley Row and Ladbroke Road right down to just to the north of Tinsley Green, but included only just a narrow strip of Haroldslea and a bit of Burstow near Peeks Brook Lane. Indeed, it is quite probable that Thunderfield Common originally included a much larger area of land. It is named in Anglo Saxon documents dating back to 880.
Thunderfield Common belonged to Chertsey Abbey, and was described in their records as 3,000 acres in [the manor] of Sutton with a den for pigs. Some of the Abbey’s documents are believed to be forgeries so nothing is certain.
To sum up: Thunderfield refers to an ancient common which was used to graze pigs. The modern town of Horley is built on this common, and there is no known connection with the moat in Haroldslea, which possibly was the site of a manor house.
Peter C. Cox.
For more details of other moats and castles see:http://www.castleuk.net/castle_lists_south/187/thunderfieldcastle.htm