Mesopotamian merchants spread their commercial institutions far and wide, into Western Asia, Egypt and Europe. The ancient inhabitants of Babylonia used the word qaqqadum, 'head', in the sense of 'principal'... our English word 'capital' (via Latin caput [head]) reflects ancient Mesoptamian usage.... our financial system, that reckons with interest on principal, harks back to the land between the Tigris and Euphrates rivers.

Introduction - Adventures in the Nearest East (1957)