But luckily in one sense, and in another unluckily, for Rome, there was an endless supply of labour to be had, of every quality and capacity, for the very same abnormal circumstances which had created the demand also provided the supply.
The great wars and the wealth accruing from them in various ways had produced a capitalist class in need of labour, and also created a slave-market on a scale such as the world has never known before or since.
Ever since the time of Alexander and the wars of his successors with each other and their neighbours, it is probable that the supply of captives sold as slaves had been increasing; and in the second century B.C.the little island of Delos had come to be used as a convenient centre for the slave trade.

Strabo tells us in a well-known passage that 10,000 slaves might be sold there in a single day.[307] But Rome herself was in the time of Cicero the great emporium for slaves; the wars which were most productive of prisoners had been for long in the centre and the west of the Mediterranean basin.

All armies sent out from Rome were accompanied by speculators in this trade, who bought the captives as they were put up to auction after a battle, and then undertook the transport to Rome of all who were suited for employment in Italy or were not bought up in the province which was the seat of war.

The enormous number of slaves thus made available, even if we make allowance for the uncertainty of the numbers as they have come down to us, surpasses all belief; we may take a few examples, sufficient to give some idea of a practice which had lasting and lamentable results on Roman society.
After the campaign of Pydna and the overthrow of the Macedonian kingdom, Aemilius Paullus, one of the most humane of Romans, sold into slavery, under orders from the senate, 150,000 free inhabitants of communities in Epirus which had sided with Perseus in the war.[308] After the war with the Cimbri and Teutones, 90,000 of the latter and 60,000 of the former are said to have been sold;[309] and though the numbers may be open to suspicion, as they amount again to 150,000, the fact of an enormous capture is beyond question.

Caesar, like Aemilius Paullus one of the most humane of Romans, tells us himself that on a single occasion, the capture of the Aduatuci, he sold 53,000 prisoners on the spot.[310] And of course every war, whether great or small, while it diminished the free population by slaughter, pestilence, or capture, added to the number of slaves.