 The concept (but not the actual combinations) is derived from Classical Latin, which used, for example, "TH", "PH", and "CH" when transliterating the Greek letters "θ", "ϕ" (later "φ"), and "χ".These were once aspirated sounds in Greek before changing to corresponding fricatives, and the "H" represented what sounded to the Romans like an following , , and respectively.Some of the digraphs used in modern scripts are