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Many smaller clans mentioned within early literature seem to have been present across the rest of the subcontinent. Some of these kings were hereditary; other states elected their rulers. Early "republics" such as the Vajji (or Vriji) confederation centered in the city of Vaishali, existed as early as the 6th century BCE and persisted in some areas until the 4th century CE. The educated speech at that time was Sanskrit, while the languages of the general population of northern India are referred to as Prakrits. Many of the sixteen kingdoms had coalesced to four major ones by 500/400 BCE, by the time of Gautama Buddha. These four were Vatsa, Avanti, Kosala, and Magadha. The Life of Gautam Budhha was mainly associated with these four kingdoms.

What was the general population's common language ?
Prakrits