Cohesion

Euripides, Suppliant Women 312-313 (tr. David Kovacs):

It is the decent observance of the laws that holds together all human communities.

           τὸ γάρ τοι συνέχον ἀνθρώπων πόλεις
τοῦτ' ἔσθ', ὅταν τις τοὺς νόμους σῴζῃ καλῶς.

Sextus Empiricus, Against the Professors 2.31 (tr. R.G. Bury):

For the laws are what bind cities together.

οἱ γὰρ νόμοι πόλεών εἰσι σύνδεσμοι.