Archaeological samples of the gun, specifically the hand cannon (huochong), have been dated starting from the 13th century. The oldest extant gun whose dating is unequivocal is the Xanadu Gun, so called because it was discovered in the ruins of Xanadu, the Mongol summer palace in Inner Mongolia. The Xanadu Gun is 34.7 cm in length and weighs 6.2 kg. Its dating is based on archaeological context and a straightforward inscription whose era name and year corresponds with the Gregorian Calendar at 1298. Not only does the inscription contain the era name and date, it also includes a serial number and manufacturing information which suggests that gun production had already become systematized, or at least become a somewhat standardized affair by the time of its fabrication. The design of the gun includes axial holes in its rear which some speculate could have been used in a mounting mechanism. Like most early guns with the possible exception of the Western Xia gun, it is small, weighing just over six kilograms and thirty-five centimeters in length. Although the Xanadu Gun is the most precisely dated gun from the 13th century, other extant samples with approximate dating likely predate it.