A family member asked me why the English language has the letter "C" when it sounds like "K", e.g. "carp", "clown", or "public", or the letter "S", e.g. "publicity" or the second "c" in "cache", when it appears in words. She wanted to know why we didn't just dispense with the letter altogether. So I did a little online searching with Google and found an explanation at the history of the letter 'C'.
The explanation was that it derives from the Roman use of the letter C to stand for the K sound. The Anglo-Saxons in what is now Great Britain adopted the Roman system. After the Battle of Hastings in which William the Conqueror defeated the Anglo-Saxon forces led by Harold Godwinson many French words became part of the English language. The Norman French pronounced "C" as "S" before the letters "I,E,(Y)". So "C" became a letter with two sounds.