Mail (also maille), often given as chain mail or chain maille, though this is a modern usage) is a type of armour or jewelry that consists of small metal rings linked together in a pattern to form a mesh. This construction can ward off a slashing blow by an edged weapon, preventing it from cutting through to the skin. It was also reasonably effective against most arrowhead types but it has several disadvantages. A well armed lance or spear, or an arrow with a narrow pointed head called a bodkin may burst the rings apart, and a heavy axe or sword blow may separate the chain links. The flexibility of mail meant that a particularly strong blow would often transfer to the user, often causing fractures or serious bruising. It is to be considered however, that most Medieval physicians or physicians of earlier time periods could usually set broken bones, but when it came to preventing infection they were woefully inadequate. Thus the mail was weak in defending against wounds which could be more easily mended but strong against those to which the soldier was most vulnerable. The word chainmail is of relatively recent coinage, having been in use only since the 1700s, prior to this it was referred to simply as mail.

The word itself refers to the armour material, not the garment made from it. A shirt made from mail is a hauberk, if knee-length; haubergeon if mid-thigh length, and byrnie if waist-length. Mail leggings are called chausses, mail hoods coif and mail mittens mitons. A mail collar hanging from a helmet is camail or aventail. A mail collar worn strapped around the neck was called a pixane or standard.

Mail was invented some time in the mid 1st millennium BC, but it is unknown where and by whom it was first used. It may have been invented independently in Japan and in Europe. The earliest finds are probably from a 5th century BC Celtic chieftain's burial located in Ciumesti, Romania. The Greek term, cataphract, came to be associated with heavy cavalry as opposed to light mounted archers. The Roman Republic first came into contact with mail fighting the Gauls in Cisalpine Gaul, now Northern Italy. The Roman army adopted the technology for their troops in the form of the lorica hamata which was used as a primary form of armour through the Imperial period where it was used alongside the lorica segmentata.

The use of mail was prominent throughout the High Middle Ages, and reached its apex in the 13th century, when full body suits of mail armour were developed. In the 14th century, plate armour began to supplement mail. Eventually mail was supplanted by plate for the most part. However, mail was still widely used by many soldiers as well as brigandines and padded jacks. These three types of armour made up the bulk of the equipment used by soldiers with mail being the most expensive. It was quite often more expensive than plate armour. A mail shirt interwoven between two layers of fabric is called jazzeraint, and can be worn as protective clothing.

The Japanese used mail (kusari) in a limited fashion in armor beginning during the Nambokucho period (1336-1392). Two primary weave methods were used: a square 4-in-1 pattern (so gusari) and a hexagonal 6-in-1 pattern (hana gusari). Kusari was typically made with rings that were much smaller than their European counterparts, and on a much smaller scale - rather than creating full garments of mail, small sections were used to link together plates and to drape over vulnerable areas such as the underarm. The rings were not welded shut, though some pieces were constructed of rings that consisted of two or more turns, similar to the modern split ring commonly used on keychains. The rings were lacquered to prevent rusting, and was always stitched onto a backing of cloth or leather. The kusari was sometimes concealed entirely between layers of cloth or leather.

Source: Wikipedia