Our letter c comes from the Roman alphabet and is a descendant of Greek gamma, which the Romans adapted and used to represent the sound (k) as well as (g). (Later they developed the form G and assigned the (g) sound to it.) In Latin and the Romance languages the pronunciation of (k) before e, i, and y gradually changed, resulting in the sound (ch) or the “soft” c pronounced like (s). Middle English scribes continued the use of soft c before e, i, and y in words borrowed from French and began to use k more frequently for the hard c sound before these vowels in native English words. In Modern English, c is, with very few exceptions, soft before e, i, and y and hard before a, o, u, and consonants.
