Chainmail , also known as chain mail, chain maille, or just mail or maille, is a type of armor or jewelry that's made from small metal rings linked together in a pattern. Mail can generally be punctured by a spear or cut by the blow from a heavy axe or sword. Its flexibility and ability to expand means that its wearer is vulnerable to blunt weapons.

However, it was an effective defense for its ability to stop cutting weapons from piercing the skin. The word chainmail is of relatively recent origin, having been in use only since the 1700s. Prior to this it was simply referred to as mail.

The word "mail" refers to the armor material, not the garment made from it. A shirt made from mail is hauberk, if knee-length; haubergeon if waist-length. Mail socks are called chausses, a mail hood is a coif and mail mittens are mitons'. A mail collar hanging from a helmet is a aventail.

Samples of mail go back as far as the Etruscans,  over 3000 years ago.  Etruscan constructed in a pattern that is more closely related to Japanese patterns than the common European 4-in-1 pattern. Because the Etruscan Mail pattern is more akin to Japanese patterns and because historical examples of mail don't appear for another 2000 years, it's assumed that Etruscan mail isn't the base for European mail. Most scholars believe that European mail developed from a ring Lamellar type of armor.

Around the 2nd Century B.C. the Romans found that the Gauls wore the first known examples of European pattern mail shirts and soon adopted it as a common armor for their secondary troops. Roman mail shirts were referred to as Lorica Hamata.

Lorica Hamata is interesting in that half of the links that made up the shirt were solid rings  punched from metal sheets. This technique continued in some later European Mail examples but most European mail is made fully from drawn-wire links. Another example of mail with punched links is called "theta" or "bar link" which comes from Persia and India. It's called "theta" or "bar link" because the punched links have a bar across their center which makes them resemble the Greek letter "theta".

From 200 B.C. through the fall of the Roman Empire and into the Dark Ages, mail was a common armor all over Europe even down into what we now call the Middle East, north into the Viking Cultures and even in the far east where the Japanese developed their own styles of mail.

Chainmail armor in the Middle Ages was achieved through a process of creating wire from steel. Once the wire portion of the process was complete, the blacksmith would form them into little interlocking rings through the use of a hand-cranked machine. The most common form of chainmail armor utilized an overlapping ring system in which rows of rings were interlinked for strength. Flat rings were thinner in one direction than the other, which meant that they had less of a tendency to open up when struck with the tip or side of a sword. The chain mail metal heated and cooled quickly and was constructed over an open flame. Inserting the actual rings was a tedious process requiring more than one person to help. About 40,000 rings were required to make one shirt of chainmail armor.

In Europe, as plate armor began to develop, it became common to use mail to protect areas that needed more flexibility than the rigid metal allowed. Mail became common in elbow joints, knees and etc. It wasn't long before full plate armor became more popular and, with the invention of fully articulated joints, mail started to loose its popularity.

Another type of mail is Japanese mail. Common Japanese patterns were lighter and more open than European, but were made of superior quality tempered wire that wasn't riveted. Some links in Japanese mail were double or even triple wrapped for strength. Like the best European mail makers, the Japanese paid attention to which parts of the body the armor was supposed to be protecting. Mail over one's chest would be thick and strong, but on an elbow where flexibility was more important, it would be lighter.

It's not really fair to compare Europe to Japan, as the fighting styles of each evolved differently. European armor needed to be heavier to deal with the bigger, crushing weapons common in their battles. Japanese combat techniques used lighter, faster weapons where mobility was more of a concern.

The Japanese were also used mail as decoration or in combination with plates. The Japanese word for chain is Kusari and each of their patterns had its own proper name. The common 4-in-2 square Japanese pattern is called Hitoye-Gusari. A similar 6-in-2 hexagonal Japanese pattern is called Hana-Gusari.

Mail is still being used today by a few industries. Butchers commonly wear fine mail gloves to protect their hands while shark divers wear entire suits of fine mail. This fine mail is made from strong, welded links and is woven on large machines.