Gillespie Moat is a large motte standing in parkland at the west end of Biggar.

Exactly when the first castle was built on this motte is unknown. One reference suggests that Baldwin Flandrensis, also known as Baldwin de Biggar or Baldwin of Biggar, built a castle here around 1150, presumably known as Biggar Castle (although there was a later Biggar Castle further to the east). The name Gillespie probably refers to George Gillespie who bought parts of the Biggar estate from the Elphinstone-Fleming family in the 1820s.

What is known is that during the second quarter of the 12th century Baldwin was granted land by David I at Biggar. Baldwin was the great grandson of Erkenbald Flandrensis of Rouen, a Norman knight who had travelled to England with William the Conqueror, and was the progenitor of the Fleming name in Scotland.

The barony of Biggar is said in some sources to have passed by marriage to the Fleming family in the thirteenth century, while other sources assert that it was in the possession of Baldwin in the 12th century.

The motte stands to a height of around 6.0m, and would have commanded good views over the surrounding area, although these have become somewhat obscured by the growth of the town. Originally, and until the 19th century, it was apparently possible to see the mottes of Roberton, Coulter and “Bamphlet” (presumably referring to Bamflatt and the Round Knowe there). The motte seems to have been flattened slightly some time since 1867, as a sketch from that year shows a taller motte with steeper sides.

The top of the motte is approximately rectangular in shape, measuring around 34.0m east to west by around 20.0m north to south. Around the base of the motte, the circumference of which is approximately 145.0m, are slight traces of a surrounding ditch, although any external defences have been obliterated or modified beyond recognition by the development of roads to the south and east, the landscaping of parkland to the west, and the construction of the manse to the north.

When viewed from the west it becomes clear that the motte is at the south end of a raised ridge of glacial material, upon which now stand the manse and Moat Park Church. It may be that this ridge formed the bailey of the castle.

The fate of the castle here is unknown. Baldwin was made Sheriff of Lanarkshire in 1162, and the royal castle of Lanark became his headquarters. The castle on the motte continued to be a residence of the Fleming family until they built Boghall Castle, possibly in the 13th century, and it may be that this site was abandoned at that time.

Little else is written about the motte, except that it was fortified by the Home Guard during the Second World War.