Along­side those early account­ing sys­tems, the Meso­pot­ami­ans developed the world's first spread­sheets, as well as soph­ist­ic­ated bank­ing sys­tems. They also inven­ted the concept of credit -- and, with it, interest-bear­ing loans. As early as the third mil­len­nium BC, grid-like tab­lets recor­ded loans of grain from the palace to the temple, enabling lenders to keep tabs on how much was repaid and what was still owed. A series of sur­viv­ing tab­lets detail how the royal granar­ies of Lagash -- a city-state sited between the sites of mod­ern Bagh­dad and Basra -- sup­plied the White Temple, which failed to repay the full amount of grain the fol­low­ing year, neces­sit­at­ing the record­ing of a defi­cit on the loan.

Temples func­tioned as banks, lend­ing sil­ver and bar­ley at dis­coun­ted rates in times of need. They also fin­anced com­mer­cial ven­tures, char­ging annual interest at 33 per cent on bar­ley. The private sec­tor took off in the early second mil­len­nium BC, with fully fledged private enter­prises in which people could invest. Assyr­ian mer­chants organ­ised trad­ing part­ner­ships to fin­ance their trips to Anato­lia, where they sold tex­tiles made by their wives at home. Traders were keen to invest their profits and not let their sil­ver lie idle. Pre­cious metals sit­ting in the money bag rather than being put to work increas­ing their value were described as 'get­ting hungry'.

The Baby­lo­nian word for interest, which trans­lates as ' increase', ori­gin­ally referred to herds of anim­als. Just as the flocks would repro­duce and mul­tiply over time, money and debt could also bur­geon. Given the huge interest rates levied by lenders, profits could grow quickly. But so could debts -- and ordin­ary people who found them­selves unable to repay their cred­it­ors were some­times enslaved.

In the second mil­len­nium BC, Baby­lo­nian kings fre­quently had to pro­claim debt amnesties to provide relief. National defi­cits also caused prob­lems. The first doc­u­mented war in his­tory, between the Sumerian cit­ies of Lagash and Umma, a little to the north­w­est, flared up over a refusal to repay a loan. The con­flict, which dragged on for 150 years (c2500--2350 BC), was a con­vo­luted tale of claim, coun­ter­claim, and battles won and lost -- all over a dis­pute over a loan agree­ment based on a rich strip of fer­tile ter­rit­ory, the Gu'edena or 'edge of the plain'.

So you can thank the Meso­pot­ami­ans for your credit card -- and also be grate­ful that interest rates have, by and large, fallen in the past 4,000 years.