The Spirit of Laws by Montesquieu

Originally published anonymously partly because Montesquieu's works were subject to censorship, Montesquieu spent nearly twenty years researching and writing THE SPIRIT OF LAWS. Montesquieu advocates constitutionalism and the separation of powers, the abolition of slavery, the preservation of civil liberties and the rule of law, and the idea that political and legal institutions ought to reflect the social and geographical character of each particular community.