Public water-mills, however, appear for the first time under Honorius and Arcadius; and the oldest laws which mention them, about the year 398, show clearly that they were then a new establishment, which it was necessary to secure by the support of government; and the orders for that purpose were renewed and made more severe by Zeno towards the end of the fifth century408. It is worthy of remark, that in the whole code of Justinian one does not find the least mention of wooden pales or posts, which occur in all the new laws; and which, when there were several mills situated in a line on the same stream, occasioned so many disputes. The mills at Rome were erected on those canals which conveyed water to the city; and because these were employed in several arts, and for various purposes, it was ordered that by dividing the water the mills should be always kept going. The greater part of them lay under Mount Janiculum409; but, as they were driven by so small a quantity of water, they probably executed very little work; and for this reason, but chiefly on account of the great number of slaves, and the cheap rate at which they were maintained, these noble machines were not so much used, nor were so soon brought to perfection as they might have been. It appears, however, that after the abolition of slavery they were much improved and more employed; and to this a particular incident seems in some measure to have contributed.
When Vitiges, king of the Goths, besieged Belisarius in Rome, in the year 536, and caused the fourteen large expensive aqueducts to be stopped, the city was subjected to great distress; not through the want of water in general, because it was secured against that inconvenience by the Tiber; but by the loss of that water which the baths required, and, above all, of that necessary to drive the mills, which were all situated on these canals. Horses and cattle, which might have been employed in grinding, were not to be found: but Belisarius fell upon the ingenious contrivance of placing boats upon the Tiber, on which he erected mills that were driven by the current. This experiment was attended with complete success; and as many mills of this kind as were necessary were constructed. To destroy these, the besiegers threw into the stream logs of wood and dead bodies, which floated down the river into the city; but the besieged, by making use of booms, to stop them, were enabled to drag them out before they could do any mischief410. This seems to be the invention of floating-mills, at least I know of no other. It is certain that by these means the use of water-mills became very much extended; for floating-mills can be constructed almost upon any stream, without forming an artificial fall; they can be stationed at the most convenient places, and they rise and fall of themselves with the water. They are however attended with these inconveniences, that they require to be strongly secured; that they often block up the stream too much, and move slowly; and that they frequently stop when the water is too high, or when it is frozen.
After this improvement the use of water-mills was never laid aside or forgotten: they were soon made known all over Europe; and were it worth the trouble, one might quote passages in which they are mentioned in every century. The Roman, Salic, and other laws411 provided security for these mills, which they call molina or farinaria; and define a punishment for those who destroy the sluices, or steal the mill-irons (ferramentum). But there were water-mills in Germany and France a hundred years before the Salic laws were formed. Ausonius, who lived about the year 379, mentions some which were then still remaining on a small stream that falls into the Moselle, and which were noticed also by Fortunatus412, in the fifth century. Gregory of Tours, who wrote towards the end of the sixth century, speaks of a water-mill which was situated near the town of Dijon; and of another which a certain abbot caused to be built for the benefit of his convent413. Brito, who in the beginning of the thirteenth century wrote in verse an account of the actions of Philip Augustus king of France414, relates how by the piercing of a dam the mills near Gournay (castrum Gornacum or Cornacum) were destroyed, to the great detriment of the besieged. In the first crusade, at the end of the eleventh century, the Germans burned in Bulgaria seven mills which were situated below a bridge on a small rivulet, and which seem to have been floating-mills415. In deeds of the twelfth and thirteenth century, water-mills are often called aquimollia, aquimoli, aquismoli, aquimolæ416. Petrus Damiani, one of the fathers of the eleventh century, says, “Sicut aquimolum nequaquam potest sine gurgitis inundantia frumenta permolere, ita, &c.417”
At Venice and other places, there were mills which righted themselves by the ebbing and flowing of the tide, and which every six hours changed the position of the wheels. Zanetti418 has shown, from some old charters, that such mills existed about the year 1044; and with still more certainty in 1078, 1079, and 1107. In one charter are the words: Super toto ipso aquimolo molendini posito in palude juxta campo alto; where the expression aquimolum molendini deserves to be particularly remarked, as it perhaps indicates that the mill in question was a proper grinding-mill. Should this conjecture be well-founded, it would prove that so early as the eleventh century water-mills were used not only for grinding corn, but for many other purposes.
It appears that hand- and cattle-mills were everywhere still retained at private houses a long time after the erection of water-mills. We read in the Life of St. Benedict, that he had a mill with an ass, to grind corn for himself and his colleagues. Among the legendary tales of St. Bertin, there is one of a woman who, because she ground corn on a fast-day, lost the use of her arm; and of another whose hand stuck to the handle, because she undertook the same work at an unseasonable time. More wonders of this kind are to be found at later periods in the Popish mythology. Such small mills remained long in the convents; and it was considered as a great merit in many ecclesiastics, that they ground their own corn in order to make bread. The real cause of this was, that as the convents were entirely independent of every person without their walls, they wished to supply all their wants themselves as far as possible; and as these lazy ecclesiastics had, besides, too little labour and exercise, they employed grinding as an amusement, and to enable them to digest better their ill-deserved food. Sulpicius Severus419 gives an account of the mode of living of an Eastern monk in the beginning of the fifth century, and says expressly that he ground his own corn. Gregory of Tours mentions an abbot who eased his monks of their labour at the hand-mill, by erecting a water-mill. It deserves here to be remarked, that in the sixth century malefactors in France were condemned to the mill, as is proved by the history of Septimina the nurse of Childebert420.
The entrusting of that violent element water to support and drive mills constructed with great art, displayed no little share of boldness; but it was still more adventurous to employ the no less violent but much more untractable, and always changeable wind for the same purpose. Though the strength and direction of the wind cannot be any way altered, it has however been found possible to devise means by which a building can be moved in such a manner that it shall be exposed to neither more nor less wind than is necessary, let it come from what quarter it may.
It is very improbable, or much rather false, that the Romans had wind-mills, though Pomponius Sabinus affirms so, but without any proof421. Vitruvius422, where he speaks of all moving forces, mentions also the wind; but he does not say a word of wind-mills; nor are they noticed either by Seneca423