Some of the most important evidence about life in ancient Babylon comes from legal documents, which provide first-hand information about the legal relationships between its inhabitants. Although not everything of importance was set down in writing, the most important obligations were embodied in written records, which make reference to both customary and statutory law. As well as the legal formalities and the names of the parties, they also bear the names of witnesses and often also that of the writer of the text, to avoid dispute. It was also important to protect the tablets - generally of unfired clay - from subsequent alteration. To do this they were clad in a clay envelope, on which not only was the contract inscribed once again (even in a variant version), but this surface was much more importantly used to impress the seals of the parties and the witnesses, whose names might sometimes also be inscribed there. Should a dispute arise, the contract could only be used in proof if this envelope was undamaged.