Õdachi

Odachi, meaning "Great/Sacred sword", was a type of long Japanese sword. The term nodachi, or "field sword", which refers to a different type of sword, is often mistakenly used in place of odachi. It is historically known as otachi.

The character for o (大) means "big" or "great". The characters for da (太) and chi (刀) are the same as tachi (太刀), the older style of sword/mounts that predate the katana. The chi is also the same character as katana (刀) and the ta in nihontō (日本刀 "Japanese sword"), originally from the Chinese character for a knife, dao.

To qualify as an odachi, the sword in question must have a blade length over 3 feet (91.44 cm). Regardless of size, most odachi have religious inscriptions on the tang. However, as with most terms in Japanese sword arts, there is no exact definition of the size of an odachi.

Purpose

The purpose of the odachi can be categorized as follows:

As an offering to a shrine or gods. Some odachi were dedicated with prayer to win a war, others were placed in shrines as legendary swords from mythology.
As a weapon. From explanations in old texts, such as Heike-monogatari, Taihei-ki tell us that odachi were used by soldiers during battles.
As a symbol for an army. Some odachi are too long for practical use. They cannot be used in a battle but it is said that they could have been used as a symbol of an army, such as flags and spears.
As a trend during a certain period. Some swords were also used for ceremonies.
To show the swordsmith's skill.

Most odachi were used for the first two reasons.

Production

Odachi are difficult to produce because their length makes heat treatment in a traditional way more complicated: The longer a blade is, the more difficult (or expensive) it is to heat the whole blade to a homogenous temperature, both for annealing and to reach the hardening temperature. The quenching process then needs a bigger quenching medium because uneven quenching might lead to warping the blade. The method of polishing is also different. Because of their size, odachi are usually hung from the ceiling or placed in a stationary position to be polished, unlike normal swords which are moved over polishing stones.

Acquiring an odachi would be hard as they would almost certainly have to be custom-made. As such, a local government or religious organization would have to fund odachi production, as there is no reason for its creation otherwise.

They are still made on occasion. One such sword, made in 1971, (now in a private collection in Texas) was made at the request of a dying man. Its purpose was to please the gods and enlist their protection of his family after his impending death.

Method of use

Odachi that were used as weapons were too long for samurai to carry on their waists like normal swords. There were two methods in which they could be carried.

One method was to carry it on one's back. However, this was seen impractical as it was impossible for the wielder to draw it quickly.
The other method was simply to carry the odachi by hand. The trend during the Muromachi era was for the samurai carrying the odachi to have a follower to help him draw it.

Odachi swordplay styles focused on downward cuts and different wields than those of normal swords.

The odachi's importance died off after the Osaka-Natsuno-Jin war of 1615 (the final battle between Tokugawa Ieyasu and Toyotomi Hideyori). Since then it has been used more as a ceremonial piece.

Reasons for loss of popularity

Battles in fields did not occur after 1615.
The Bakufu government set a law which prohibited holding swords above a set length (in Genna 3 (1617), Kan'ei 3 (1626) and Shoho 2 (1645)).

After the law was put into practice, odachi were cut down to the shorter legal size. This is one of the reasons why odachi are so rare. odachi were no longer of practical use, but were still made as offerings to Shinto shrines. This became their main purpose. Due to the amount of skill required to make one it was considered that their awesome appearance was suitable for praying to the gods.