In order to keep a secure transaction, the tokens were sealed inside a clay envelope. The outside of the envelope was marked with the tokens, so the owner would know what was inside without breaking it open. By 3,000BC, these marks evolved into complex systems of numbers, capable of recording very large quantities of goods, but over the following 500 years, writing gradually developed into cuneiform and the number systems developed into 'arithmetic'. By 2,000BC, there was a fully-developed mathematics system, of which thousands of clay tablets have been found. The earliest cylinder seals to be found date from 3,500BC and were considered valuable, especially those made from semi-precious stone.
Cylinder seals are small cylinder-shaped objects which has a carved scene or design.
When it is rolled on wet clay it leaves a 'print' and can be reproduced many times. The average cylinder is about 2.5cm high and 1.5cm in diameter. They were usually made out of stone, but metal, ivory, wood, bone, shell and baked clay also used. The seals were used to mark ownership of property. Legal and commercial documents were written on clay tablets and the engravers name was shown on the imprint of a cylinder seal.