Elsewhere in this atlas the Latin C's sound is traced back to Phoenician gimel by way of Greek gamma; here the story is what happened to gimel's other letter. Etruscan, the language Rome's alphabet passed through, had no voicing distinction between k and g, so its scribes used a single rounded letter, descended from Greek gamma, for both sounds.
Rome inherited that ambiguity along with the alphabet itself, and for the first few centuries of Latin writing C did double duty for k and g alike, visible in early inscriptions and in the abbreviations C. and Cn. for the personal names Gaius and Gnaeus, which preserve the old hard-g pronunciation of C. The ambiguity was resolved only around 230 BCE, when, tradition holds, the scribe Spurius Carvilius Ruga added a short stroke to C to create a distinct letter for the voiced sound, G. With G handling voiced /g/, C settled into its modern role as the letter for /k/. C also does double duty as a Roman numeral, worth one hundred; the standard account holds this value was later reinforced, if not fully caused, by C being the first letter of the Latin word centum, hundred, an association the numeral system's other large values, D and M, echo in their own way.