K's history in Latin is essentially one of near-disappearance and partial return. The letter descends, like C and G, from a Phoenician sign, in this case kaph, transmitted through Greek kappa, and the earliest Etruscan and Roman alphabets included it in its own right. Once C had absorbed the /k/ sound for ordinary Latin use, as covered elsewhere in this atlas, K became almost entirely redundant, and classical Latin kept it only in a handful of fossilised abbreviations, most famously Kalendae, the first day of the Roman month, from which the modern word calendar descends, and a few personal names such as Kaeso. Ordinary Latin vocabulary used C instead throughout the classical period, and K's near-total disuse continued through much of the Middle Ages in the Romance languages descended from Latin, which mostly avoid the letter to this day outside loanwords.
English and the Germanic languages, by contrast, kept K in regular use for the hard /k/ sound before front vowels, a role C could not reliably fill once its own pronunciation began shifting toward /s/ before e and i in French and, through Norman influence, in English. K's angular shape has remained essentially unchanged since its Phoenician origin, since it dropped out of Latin's cursive tradition too early to undergo the shape splits seen in letters such as C, I or U.