Tenants had a threefold obligation related to their landholding; the so-called ???common burdens' of military service, fortress work, and bridge repair.[7][8] And over time the hide was given a set acreage, in the Domesday book the most common size, in use was 120 acres (48.56 ha; 0.19 sq mi).[7][9] However some areas such as Dorset and Wiltshire used units based on 40 acres (16.19 ha; 0.06 sq mi)