LI. The threshing floor should be on high ground so that the wind can blow upon it from all directions. It should be constructed of a size proportioned to your crops, preferably round and with the centre slightly raised so that if it rains the water may not stand on it but drain off as quickly as possible, and there is no shorter distance from the centre to the circumference of a circle than a radius:[98] it should be paved with well packed earth, best of all of clay, so that it may not crack in the sun and open honeycombs in which the grain can hide itself, and water collect and give vent to the burrows of mice and ants. It is the practice to anoint the threshing floor with amurca,[99] for that is an enemy of grass and a poison to ants and to moles. Some build up and even pave their threshing floor with rock to make it permanent, and some, like the people of Bagiennae, even roof it over because in that country storms are prevalent at the threshing season. In a hot country where the threshing floor is uncovered it is desirable to build a shelter near by where the hands can resort in the heat of the day. _Threshing and winnowing_ LII. The heaviest and best of the sheaves should be selected on the threshing floor and the spikes laid aside for seed. The grain is threshed from the spikes on the threshing floor, an operation which some perform by means of a sledge drawn by a yoke of oxen: this sledge consisting of a wooden platform, studded underneath with flints or iron spikes, on which either the driver rides or some heavy weight is imposed in order, as it is drawn around, to separate the grain from the chaff: others use for this purpose what is called the punic cart, consisting of a series of axle trees, equipped with toothed rollers, on which some one sits and drives the cattle which draw it, as they do in hither Spain and other places. Others cause the grain to be trodden out under the hoofs of a herd of driven cattle, which are kept moving by goading them with long poles. When the grain has been threshed it should be tossed from the ground by means of a winnowing basket or a winnowing shovel when the wind is blowing gently, and this is done in such way that the lightest part, which is called the chaff, is blown away beyond the threshing floor, while the heavy part, which is the corn, comes clean into the basket.[100] _Gleaning_ LIII. After the harvest is over the grain fields should be gleaned of shattered grain, and the straw left in the field should be gathered and housed, but if there is little to be gained by such work, and the expense is disproportionate, the stubble should be grazed: for in farming it is of the greatest importance that the expense of an operation shall not exceed the return from it. _Of the vintage_