The yojana was the longest unit of linear measurement employed in ancient India. It indicated a length that is calculated to have been on the order of 7-8 kilometers, and was broken down into eight krosas, the next smallest ancient Indian unit of measure (which was approximately equal to a kilometer; most likely, a bit smaller).

Linguistically, the word yojana is derived from the same root that gives us both the English word "yoke" and the Indian term "yoga". It is thought that "yojana" initially meant "being yoked", and that it was used as a unit of measure to indicate the approximate distance that a cow could pull a cart to which it was yoked.

The yojana is used extensively in ancient descriptions of Buddhist cosmology (and, presumably, Hindu cosmology as well). The size of layers of the Earth, the heights of mountains, and the depths of seas are all described using yojanas, so understanding this term is important for comprehending the scale and detail that the ancient thinkers employed. Mount Meru, for instance, the axis mundi of the ancient Indian world, was described as being 160,000 yojanas high, of which half was beneath the water. This gives Sumeru a height of approximately 560,000 kilometers- taller than any actual mountain in the Himalayas, or anywhere else in the world. This indicates the cosmic size and power of Mt. Meru, and makes it clear that it is likely a purely philosophical concept, rather than an encoding of an actual mountain into mythology.

Some other Ancient Indian units of measure:

These examples and calculations are all borrowed from Akira Sadakata's excellent book Buddhist Cosmology: Philosophy and Origins. It is, sadly, out of print and difficult to find, but is the finest resource I've ever encountered for learning about the worldviews of ancient Buddhist and Indian civilization. If you find this ancient table of conversion uninteresting, I encourage you to skip to the end; all will be made clear.

Particulate Measures
  • A paramanu is the smallest, indivisible particle of matter. An atom.
  • Seven paramanu for an anu, meaning minute.
  • Seven anu form a loha-rajas, a "gold dust mote" (gold was thought to be a very fine material, and as such its particulate elements were very small.)
  • Seven loha-rajas makes a "water droplet" (ab-rajas), the smallest measurable quantity of water.
  • Seven water droplets is a speck of dust the width of a rabbit hair (sasa-rajas)
  • Seven of these made a mote of dust the width of a sheep's hair (avi-rajas).
  • Seven avi-rajas make a mote of dust the width of a cow's hair. Seven of these make a spot of dust that can be seen in a beam of sunlight shining through a chink in the wall (chida-rajas).
  • Seven chida-rajas make a "louse-egg", seven of which make a louse. Seven lice makes a kernel of barley. I am not making this up.
  • Finally seven kernels of barley make a single finger joint (anguli-parvan), which is the distance between two joints of the finger.
Linnear Measures
  • A hasta, forearm, is the distance from the elbow to the tip of the finger. The hasta is 24 times the width of the finger.
  • The dhanus, bow, is the size of an ancient Indian bow. It is assumed to be approximately the length between a persons two outstretched arms, or about two meters.
  • The krosa, mentioned above, is 500 bow lengths. It had the original meaning of the sound of a cow mooing, and probably meant the distance at which a cow can be heard. Later, Buddhist interpreters called the krosa the distance between the forest and the village, and it was held to be the ideal distance for Buddhist monks to live from a village; far enough that they are not wrapped up or distracted by village life, but near enough that they can beg for alms and teach the villagers.
  • Finally, seven krosa made a yojana.

So, why is any of this tedious material important? To answer that, I quote at length from Sadakata:

A study of Indian units of measure gives us some idea of the lifestyle of the ancient Indians. Villages lay close to the forest. Cows, prized for their milk, could be heard in the distance or seen pulling carts. Barley was grown. At times the soldiers of the king would appear in the main thoroughfare of the village, armed with bows. Perhaps people sat in sunny corners and picked off lice. They were familiar with rabbits and sheep.
An entire reconstruction of ancient Indian life, made entirely from a study of units of measurement. Furthermore, we have information about how far from town monks and monasteries might have been; we have information to judge how far people traveled regularly, and how large their world was, for practical purposes. My own grandfather, a farmer in rural Kentucky, has never lived more than five miles from the house where he was born. A few generations ago, he likely would not have ever traveled farther than this distance. I think a system of measure whose largest unit encompasses approximately the same range provides some significant insight into the similarities and differences between our world and that of ancient India. Theirs was bound by the yojana, and ours is stretching towards the light year.

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