中国春秋战国和秦汉时代,常见的书信是木牍。木牍一般长1尺,约0.33米,故也叫尺牍。信封用木板制成,呈鲤鱼形,一底一盖夹在尺牍的外面,木板上刻上三道线槽,用绳子捆绕三圈,然后再穿过一个方孔缚住,在线端或交叉处加以检木,封上黏土,上盖印章,作为信验,以防私拆。这种木板可算是中国历史上最早的信封。 China Spring and Autumn Period and the Qin and Han dynasties, the common correspondence is clogs. Clogs generally 1 foot long, about 0.33 meters, it is also called Ruyi. Envelopes made of wood, was carp-shaped, one at a time covered with a cover on the outside of the ruler, engraved with three trunks on the board, tied with a rope for three laps, and then through a square hole cable live, online or cross Office to check wood, sealed with clay, seal on the seal, as a letter of inspection, to prevent the private demolition. This plank can be regarded as the earliest envelope in Chinese history.