In typography, capital letters refers to uppercase letter such as A, B, C, D, . . . etc. They are used to start sentences and the first letter of proper nouns is always capitals. In c.114 CE, on the base of a column in Trajan’s Forum, Rome, an inscription was seen chiselled into its base.  That inscription had most of the capital letters known today. All inscriptions were in capital letters, until the sixth century.