Salus populi suprema lex esto
"Let the good of the people be the supreme law" or "The welfare of the people shall be the supreme law") is found in Cicero
's De Legibus
(book III, part III, sub. VIII), as Ollis salus populi suprema lex esto
The phrase is the state motto of Missouri, accepted, like many other states, as an element of its state seal. It is also the motto, and appears on the coat of arms, of the City of Salford, the London Borough of Lewisham, the Duquesne University School of Law, and is used as the motto of the Vlaams Belang political group in the Belgian Chamber of Representatives.
John Locke uses it as the epigraph in his Second Treatise on Government and refers to it as a fundamental rule for government.