Drawing of St. Martin of Braga, Madrid, Biblioteca del Monasterio de San Lorenzo de El Escorial, Códex Albeldensis, a. 976

St. Martin of Braga, Formula honestae vitae († ca. 550 A.D.)

Quid est iustitia, nisi naturae tacita conventio, in adiutorium multorum inventa. Iustitia non nostra constitutio, sed divina lex est, vinculum societatis humanae.

What is justice but a tacit covenant (contract) of nature established for the aid of many.  Justice is not based on our statute but is a part of divine law and the bond of human society.

In the Middle Ages this work was attributed to Seneca.

Stephan  Kuttner, "A forgotten definition of justice,” Studia Gratiana 20 (1976) 73-110.