Latin, avera, averagium.
Cartage was the obligation to provide a draught animal, normally an ox; in some cases the provision of the cart itself was separately specified. In most of the recorded cases cartage was due to the sheriff. All but three of the references to cartage occurred in Cambridgeshire and Hertfordshire, two of the counties in circuit 3. It therefore seems likely that cartage was not recorded systematically and was more widespread than the record suggests.
As with many such customs, the service could be rendered in cash or kind, Domesday Book often putting a price on the obligation, normally 4d in Hertfordshire and twice that amount in Cambridgeshire.
For more detail, see Paul Vinogradoff, English society in the eleventh century: essays in English medieval history (1908); and N. Nielson, Customary rents (1910).