Titus Livius (Livy) Ab urbe condita 7.16.7

1. “One of the consuls, Cn. Manlius, was in the field with a consular army to carry on the war against the Tarquiniensians and Faliscans: his colleague, C. Marcius Rutilus was engaged with the Privernatians and enriching his army, it is said, with the plunder of the enemy's country, for many years untouched by the ravages of war. It is probable that the soldiers on this occasion made prisoners of many Privernatian families, and released them again on payment of a large ransom. But prisoners taken in war becoming, according to ancient law, the slaves of the captor, his release of a prisoner upon ransom was, in fact, the manumission of a slave. Accordingly Cn. Manlius called his soldiers together in the camp near Sutrium according to their tribes, and as they were assembled in regular comitia he proposed to them a law that five per cent. on the value of any emancipated slave should be paid by his master into the public treasury. It might be argued that the State ought not to lose all benefit from the plunder acquired by its soldiers; and that especially if a soldier set an enemy at liberty for the sake of his ransom some compensation should be made to his country whom his act might be supposed to injure. There was some plausibility in this, and the army of Manlius might have felt also some jealousy at the better fortune of their comrades, and might have known that their own general would not, like C. Marcius, give up to them the full benefit of such plunder as they might acquire from the Etruscans.” — Arnold's History of Rome, II. 78-9.