What makes the c in Caesar sound like an s?

Answer 1

This answer includes some technical terms. In Caesar's day the word Caesar was correctly pronounced KYE-SARR, but the long ae (ah+ee) diphthong was already becoming a simple eh sound in popular speech. By the post-classical period, as the popular, or 'vulgar" Latin spoken in different parts of the Roman Empire began evolving into the various Romance Languages, the K sound before a front vowel such as the eh sound in Caesar had become palatalized, pronounced like CH in English, as it remains in Modern Italian and "Church" Latin. In French, however, the palatalization went further, all the way to pronouncing the original K sound like an S before a front vowel, so that the Latin C- words (including many originally Greek K-words) we have from French, like science and cinema - and Caesar - for example, are pronounced as they are, and not as skyence and kinema and Kaiser.