Translation of the Tamil Wikipedia page
The yazh is the most important of the ancient musical instruments. Yazh means it is made of "nerves" (strings). The basic classifications of musical instruments are those made with hide, those contaning holes, those with strings and meedatru karuvi (?). Of these, the stringed instrument yazh was the first musical instrument played by Tamils.
The yazh was the first instrument based on which other stringed instruments were developed. This instrument has become completely forgotten and is basically an ancestor of the veena. Yazh is also called "kellvi" (question mark) due to its shape.
Table of Contents: 1. History 2. Development 3. Yazh and Veena 4. In literature 5. Structure 6. Structure as described in porunaraatru padai (ancient book) 7. Appearance in porunaraatru padai 8. Adiyaarku nallar (a poet)'s description 9. Types of yazh 10. How to play 11. Becoming obsolete 12. Comparison with today's yazh 13. See also 14. References
One of the instruments in use in hilly regions was the bow (?). When the bow is strung and arrow released, the sound that was made was the sorce for the creation of the yazh. This bow gave rise to the "bow lute" (vil yazh). Though the Paditrupattu (a book of poems) says that the yazh originated in forest land, its more appropriate origin is in the hilly regions because hunting was a major occupation only in hilly regions.
This vil yazh, because of human effort and labour, has multiple types.
We do not have enough sculptures or paintings today to know the exact structure of the yazh. Sangam literature (puranaanooru, kalithogai, paripadal and aatrupadai books, thirukkural, silappadhikaram, perungadai, jeevagachintamani etc. epics and spiritual literature) contain information about the yazh. Still, we can only make out the types as peri yazh (big), siri yazh (small), magara yazh (red), sakoda yazh (?) but we don't know the real structure.
Pallava temples (Kanchi Kailasnath, Rajaraja Chola's temple etc.) have yazh sculptures.
Even though the yazh originated in hilly landscapes, it spread to other regions as well. Players of this instrument were called "banars" and literature talks about them. Of the yazh players, there were two divisions - big and small yazh players. Based on the musicians there are two books in Sangam literature using which we can understand the importance of these musicians.
These books describe how the kings praised and cherished these musicians. This is an accompanying instrument while singing. From being a common man's instrument it became one worthy of worship.
Tamilians gave prime importance to music that originated from the yazh. Because of this, starting from one string, 3, 5, 7... 1000-stringed yazh came into being. Though the shape was not initially a consideration, different kinds of red yazh came into being. The yazh grew like this until the 9th century B.C. Afterwards it developed into the veena. This veena is today one of the foremost instruments in music.
Yazh and Veena
In Sangam literature and early epics, only the yazh is mentioned. Later on, in Bhakti literature, both yazh and veena are described. In Jeevagachintamani veena and yazh are described as about the same. In Silappadhikaram, Narada's veena is described as yazh.