A small, hard block that has a flat surface engraved with a design that can be transferred to soft clay or wax as a mark of ownership or authenticity. Stamp seals appear in Mesopotamia from the Halafian period in the fifth millennium BC, when they were used to impress ownership marks on lumps of clay which were then attached to goods. In the Bronze Age, it was differently shaped for different cultures: square in the Indus, round in the Persian Gulf (Barbar), and compartmented in central Asia (Bactrian). Stamp seals preceded cylinders and developed over a period of about 1,500 years until largely replaced by the cylinder in the 3rd millennium BC. Seals came into use before the invention of writing for the securing of property and the method was either to shape clay over the stopper or lid or to make a fastening with cord and place clay around the knot and then impress it with the seal. The sealing of written documents, mainly clay tablets and papyrus scrolls, became regularly established in the latter part of the 3rd millennium BC.