Mandala 7, credited to the Vasishtha family, is the largest of the six family books and among the most historically and poetically distinctive. Hymn 7.18 narrates the Battle of the Ten Kings, a coalition of tribal chieftains defeated at the Ravi river by King Sudas with Vasishtha's ritual support, the closest thing the Rig Veda offers to a datable historical event and a major source for reconstructing the political geography of the early Vedic-period Punjab.
The mandala also gives unusually sustained attention to Varuna, guardian of cosmic and moral order, including hymns of genuine ethical self-examination, "what was my chief sin, Varuna, that you seek to slay your worshipper and friend," among the closest the Rig Veda comes to personal confession of wrongdoing rather than only ritual request. Its best-known single hymn to modern readers may be 7.103, the so-called frog hymn, which compares Brahmin priests chanting together at the sacrifice, once the rains arrive, to a chorus of frogs croaking in unison after a dry season, a passage read variously as gentle satire, as a genuine nature hymn celebrating the monsoon's return, or as both at once. Vasishtha's rivalry with Vishvamitra, author of Mandala 3, is narrated within the Rig Veda itself and developed at enormous length in later epic literature.