For the age with which we are more specially concerned, we have the evidence of Varro's three books on husbandry, written in his old age, after the fall of the Republic. Here we find the economic condition of the farm little changed since the time of Cato. The permanent labour is non-free, but in spite of the vast increase in the servile labour available in Italy, there is still a considerable employment of freemen at certain times, on all farms where the olive and vine were the chief objects of culture. In the 17th chapter of his first book, in which he gives interesting advice for the purchase of suitable slaves, he begins by telling us that all land is cultivated either by slaves or freemen, or both together, and the free are of three kinds,--either small holders (pauperculi) with their children; or labourers who live by wage (conducticii), and are especially needed in hay harvest or vintage; or debtors who give their labour as payment for what they owe (obaerati).[342] Varro too, like Cato, recognises the necessity of purchasing many things which cannot well be manufactured on a farm of moderate size, and thus the landowner may in this way also have been indirectly an employer of free labour; but so far as possible the farm should supply itself with the materials for its own working,[343] for this gives employment to the slaves throughout the year,--and they should never be allowed to be idle.[344] Thus it is abundantly clear that even in the time of Cicero there was a certain demand for free labour in the ordinary Italian oliveyard and vineyard, and that the necessary supply was forthcoming, though the permanent industrial basis was non-free, and the tendency was to use slave-labour more exclusively. The rule that the slave cannot be allowed to be unemployed was a most important factor in the economical development, and drove the landowner, who never seems to have had any doubt about the comparative cheapness of slave-labour,[345] gradually to make his farm more and more independent of all aid from outside. In the work of Columella, written towards the end of the first century A.D., it is plain that the work of the farm is carried on more exclusively by slave-labour than was the case in the last two centuries B.C.[346]