In winter the cattle came down into the lowlands and grazed on the pastures near the tyddyns or homesteads of the tref, and as each of these had its corn and cattle-yard,[44] we may conclude that each owner penned in his own cattle at night during the winter months or joined with some other tribesmen who had a homestead in doing so. The rules as to the divisions of the tyddyns probably referred to these winter homesteads so held in quasi-severalty. We need not dwell upon the common _oven_. Every hamlet in Brittany possesses its common oven to this day, often in the middle of the village green. Nor need we more than mention the common plough, to the team of which the tribesmen contributed oxen for the _cyvar_ or common ploughing of the portion of the waste agreed upon for each year’s corn crop. [Sidenote: The trefgordd the unit for food rents. The tribesmen could be shifted about.] The attempt to realise what this practical unit--the trefgordd--was, will not be thrown away if it should help us to understand how easily it lent itself to the arrangement of the chieftain’s food-rents or tribute in after-times of taxation. Granted that some such system of trefgordds or clusters of trefgordds pretty generally prevailed, having grown up as a matter of convenience in a grazing community, it is obvious how easily it might become the unit of tribute or taxation. Just as in the Domesday Survey the number of ploughs affords such a unit, so in a tribal community a district might easily be fiscally estimated at so many herds, or so many churns, or so many ploughs. All these would mean so many trefgordds. And whatever the relations of the trefgordd to the villata of the surveys might be, and however much or often the actual residents, with their herds, might be shifted from one district to another, the district, as in the Denbigh Extent, would remain the permanent unit for payments. [Sidenote: The _firma unius noctis_. Afterwards commuted into money payments.] In the early stages of tribal life, when the chieftain of the tribe moved from one district to another and received his food-rents in the actual form of ‘the night’s entertainment,’ each customary place of encampment in his annual progress would become the centre at which the food-rents would be paid and services rendered for as many nights’ entertainment as his accustomed stay in the place. In later stages, when the chieftain’s dues were commuted into money, the ‘tunc pound’ in lieu of food-rents easily became, as we find it in the surveys, a charge on the district rather than on the shifting tribesmen and their herds.