The carucate was both a unit of assessment and a peasant landholding unit found in most of the Danelaw counties. The word carucate is derived from caruca, Latin for a plough. Since the standard Domesday plough team could notionally plough 120 acres in an agricultural year, the carucate was a nominal 120 acres.
These, of course, were fiscal acres which could bear a variable relationship to the customary acres on the ground. Since customary acres were normally composed of scattered furlong strips whose size varied according to the nature of the soils and the shape of the fields, carucates could vary in size from area to area, or even within the same manor.
Despite variations in size, however, individual carucates could, like other peasant holdings, remain fixed in size over generations, even centuries, their integrity maintained by the power of the lord or the customs of the manor. They provided the stable base for both the manorial and the assessment systems.
For more detail, see Frederic Seebohm, The English village community (fourth edition, 1915); J.H. Round, Feudal England (1895); F.W. Maitland, Domesday Book and beyond (1897); Reginald Lennard, 'The origin of the fiscal carucate', Economic History Review, first series, vol. 14 (1944-45), pages 51-63; Cyril Hart, The Danelaw (1992); and Rosamond Faith, The English peasantry and the growth of lordship (1997).