Mores autem neque mitissimi nec rursus truces atque crudeles, quod illi furem quoque adulantur, hi etiam domesticos invadunt. satis est severos esse nec blandos, ut non numquam etiam conservos iratius intuantur, semper excandescant in exteros. maxime autem debent in custodia vigilantes conspici nec erronei, sed adsidui et circumspecti magis quam temerarii. nam illi, nisi quod certum conpererunt, non indicant, hi vano strepitu et falsa suspicione concitantur. haec idcirco memoranda credidi, quia non natura tantum, sed etiam disciplina mores facit, ut et, cum emendi potestas fuerit, eius modi probemus et, cum educabimus domi natos, talibus institutis formemus. nec multum refert, an villatici corporibus graves et parum veloces sint; plus enim comminus et in gradu quam eminus et in spatioso cursu facere debent. nam semper circa septa et intra aedificium consistunt, immo ne longius quidem recedere debent satisque pulchre funguntur officio, si et advenientem sagaciter odorantur et latratu conterrent nec patiuntur propius accedere vel constantius adpropinquantem violenter invadunt. primum est enim non adtemptari, secundum est lacessitum fortiter et perseveranter vindicari. atque haec de domesticis custodibus, illa de pastoralibus. pecuarius canis neque tam strigosus aut pernix debet esse, quam qui dammas cervosque et velocissima sectantur animalia, nec tam obesus aut gravis quam villae horreique custos; sed et robustus nihilo minus et aliquatenus promptus ac strenuus, quoniam et ad rixam pugnamque nec minus ad cursum conparatur, cum et lupi repellere insidias et raptorem ferum consequi fugientem praedamque excutere atque auferre debeat. quare status eius longior productiorque ad hos casus magis habilis est quam brevis aut etiam quadratus, quoniam, ut dixi, non numquam necessitas exigit celeritate bestiam consectandi. ceteri artus similes membris villatici canis aeque probantur.
(Columella, De Re Rustica 7.12.5-9)
In character they should neither be very mild nor, on the other hand, savage and cruel; if they are mild, they fawn on everyone, including the thief; if they are fierce they attack even the people of the house. It is enough that they should be stern but not fawning, so that they sometimes look even upon their companions in servitude with a somewhat wrathful eye, while they always blaze with anger against strangers. Above all they should be seen to be vigilant in their watch and not given to wandering, but diligent and cautious rather than rash; for the cautious do not give the alarm unless they have discovered something for certain, whereas the rash are aroused by any vain noise and groundless suspicion. I have thought it necessary to mention these points, because it is not nature alone but education as well which forms character, so that, when there is an opportunity of buying a dog, we may choose one with these qualities and that when we are going to train dogs which have been born at home, we may bring them up on such principles as these. It does not matter much if farm-yard dogs are heavily built and lack speed, since they have to function rather at close quarters and where they are posted than at a distance and over a wide area; for they should always remain round the enclosures and within the buildings, indeed they ought never go out farther from home and can perfectly well carry out their duties by cleverly scenting out anyone who approaches and frightening him by barking and not allowing him to come any nearer, or, if he insists on approaching, they violently attack him. Their first duty is not to allow themselves to be attacked, their second duty to defend themselves with courage and pertinacity if they are provoked. So much for the dogs which guard the house; our next subject is sheep-dogs. A dog which is to guard cattle ought not to be as lean and swift of foot as one which pursues deer and stags and the swiftest animals, nor so fat and heavily built as the dog which guards the farm and granary, but he must, nevertheless, be strong and to a certain extent prompt to act and vigorous, since the purpose for which he is acquired is to pick quarrels and to fight and also to move quickly, since he has to repel the stealthy lurking of the wolf and to follow the wild beast as he escapes with his prey and make him drop it and to bring it back again. Therefore a dog of a rather long, slim build is better able to deal with these emergencies than one which is short or even squarely built, since, as I have said, sometimes the necessity of pursuing a wild beast with speed demands this. The other joints in sheep-dogs if they resemble the limbs of farm-yard dogs meet with equal approval. (tr. Edward S. Forster & Edward H. Heffner)