Note: Do not rely on this information. It is very old.
QQ, the 17th letter of our alphabet, originated in the hieroglyphic symbol of a knee. Through the Phoenician qoph it passed into the Greek alphabet as the velar guttural koppa (kw), which was afterwards supplanted by the palatal kappa (k), surviving only as the symbol for 90. But amongst the Romans, who found it in the Chalcidian alphabet of Cumae, it secured a lasting position. It made its way into Teutonic words very gradually; thus, in Middle English words of Saxon origin the sound is represented by cw till the latter part of the 13th century.
Click for more about Cumae