The earliest extant Tamil grammar book, which also provides insights into Sangam society, is:
- Tirukkural
- Tolkappiyam
- Silappatikaram
- Manimekalai
Answer: Tolkappiyam
Authored by Tolkappiyar, the 'Tolkappiyam' is not just a grammar text but a comprehensive guide to Tamil poetics, sociology, and the cultural life of the Sangam age.