How do you pronounce ‘Cicero’? With ‘s’ or with ‘k’?

Answer

In classical Latin at the time of Cicero, the only possible pronunciation was /k/. Sufficient sources indicate that the “palatalization” of /k/ for a /e/ or an /i/ occurred only much later, probably not before the 3rd century AD. This palatalization to /ts/ started with sound combinations such as -cia, -cius and -tia, -tius to -tsa, etc eg iustitia > iustitsia.

The palatalized pronunciation is a consequence of Church Latin.