Montesquieu
 

XXIII.20 That the Romans found it necessary to make laws for the propagation of the species

The Romans, by des­troying all the others, were cons­tantly des­troying them­sel­ves in action, effort and vio­lence ; they were using them­sel­ves up, like a wea­pon that is always in use.

I shall not speak here of the atten­tion they devo­ted to sup­plying them­sel­ves with citi­zens as they were losing them,1 of the asso­cia­tions they made, the pri­vi­le­ges they bes­to­wed, and that immense seed bed of citi­zens they found in their sla­ves. I shall say what they did, not to replace the citi­zens, but to replace the men ; and as they were the best peo­ple on earth for mat­ching their laws to their pro­jects, it is not indif­fe­rent to exa­mine what they did in this regard.

A modern writer [i.e., Montesquieu] has treated this in his Considerations on the Causes of the Greatness of the Romans and of their Decline, 1748.