The sixth Mandala of the Rigveda has 75 hymns, mainly to Agni and Indra. Most hymns in this book are attributed to the bārhaspatya family of Angirasas, especially to Bharadvaja. It is one of the "family books" (mandalas 2–7), the oldest core of the Rigveda, which were composed in early vedic period(1500-1000 BCE).[1]
Deities addressed besides Indra and Agni include the Vishvadevas, Pushan, the Asvins, Ushas (Dawn), the Maruts, Dyaus and Prthivi (Heaven and Earth), Savitar, Brhaspati and Soma-Rudra.
The rivers mentioned in the sixth Mandala are the Sarasvati, Yavyavati and Hariupiya. RV 6.61 is entirely dedicated to Sarasvati. In RV 6.45.31 the term Ganga occurs which refers to the River Ganges.
Talageri (2000), based on his proposition of a westward expansion early Rigvedic culture from Haryana (contrary to the nearly universally assumed eastward expansion from Gandhara) and his identification of some Rigvedic rivers, claims this Mandala as the oldest of the family books.[2]