Bulla (plural bullae, Middle Persian: gil muhrag) is the term used to refer to inscribed pieces of clay used by the Sumerians in 8th millennia B.C. They were used for agricultural transactions as a form of identification and for tamper-proofing. They served as receipts and encapsulated clay tokens that represented the quantity and types of goods borrowed. After the creation of Papyrus and parchment they developed into inscribed pieces of clay or metal used to seal documents or parcels. This suggests evidence about some of the earliest forms of specialization in the ancient world, moving from a purely agricultural society to a settled society. Therefore, it's likely only skilled and trained individuals could have created this form of administrative system.