Horace wrote his first book of Satires (meaning “medley” rather than “satire” in the modern English sense) no later than 33 BCE. In a passage in the Third Satire, he criticizes the Stoic doctrine that justice has its basis in nature. He suggests that rules are conventions that allow us to prevent conflict with minimal cruelty.

Nothing about his position is unique, but his language is luxuriant: “cum prorepserunt primis animalia terris / mutum et turpe pecus, glandem atque cubilia propter / unguibus et pugnis …” In my version …

When the animals crawled from the new* earth,
That mute and ugly herd fought for a nut 
Or a place to rest--with nail and fist, 
Then with clubs, then with tools they’d designed for war,
Until they came upon words to mark out sounds 
And sense, and names. From then on, war waned. 
They walled towns and wrote laws so that no one
Should be a thief, a thug, or an adulterer.
For even before Helen, sex** was a vile 
Cause of conflict, but those are forgotten 
Who died chasing it, like the bull in the herd, 
Cut down by someone more fit than he is.
You have to admit, if you really search the files,
That laws were contrived in fear of injustice, 
For nature can’t distinguish just from unjust
As she makes some things safe and others best to shun,
Nor can reason convince us it is just as bad--
And bad in the same way--to step on someone’s 
Garden plant as to steal a holy relic 
By cover of night.*** Let there be a standard 
To tell the right penalty, so the cruel lash 
Isn’t used when a regular beating would suffice.

Horace, Satires. 1.3.99-119, my translation

*Literally, “first earth.” **Actually a vulgar, sexist word. *** I’m surprised he doesn’t say: reason can’t convince us it is worse to steal the sacred object.

See also some thoughts on natural law; “The Wedding of Peleus and Thetis“; pragmatism and the problem of evil