As is well known, polis and imperium are the two fundamental political
models which were developed in classical times, by the Greeks and the Romans respectively.
In principle, the two models are mutually exclusive, but from Cicero’s idea
of (a sort of) ‘double – civic and imperial – citizenship’ (De legibus) on, efforts have
been made towards envisaging the possibility of some compatibility between them. On
the other hand, after Alexander’s conquest of the Persian realm, the Greek political
thought had also apparently begun to accept the idea of a political structure capable of
gathering together many different cities and peoples: a cosmopolis. This was probably
the leading idea of the Politeia written by the Stoic philosopher Zeno; or, at least, this
was the interpretation of that text proposed by Plutarch, who wrote at the beginning
of the best period of the Roman Empire. And in the generation following Plutarch,
in his Roman Oration the Smyrnean sophist Aelius Aristides went so far as to imagine
the Roman Empire as a sort of federation of poleis under the supreme direction of the
emperor. In this way, the ancient political thought tried to overcome the old dichotomy
between the two fundamentally opposed political models of polis and imperium. During
the Middle Ages, both in the Western and in the Eastern parts of the former Roman
Empire the idea of empire remained the only accepted political idea, even though, with
the twelfth and thirteenth centuries, new political structures at a civic level began to
appear in Northern and Central Italy. Rediscovering the principles of self-government,
in a way these political structures repeated the ancient polis-model. But for this model
to gain theoretical legitimization, it needed to wait for the first decades of the sixteenth
century, when Machiavelli, drawing on the ancient Latin and Greek authors, was able
to propose a new republicanism, which was to become one of the leading political ideas
of modern Europe. And now, we must once again face the ancient, Ciceronian, problem,
seeking to reconcile the two different political principles of cosmopolitanism and
civic citizenship at a global level.