[6] By the 6th century BCE, it had consolidated into one of the four great powers of ancient northern India, along with Magadha, Vatsa, and Avanti.

[8] The presence of the lineage of Ikshvaku—described as a raja in the Ṛgveda and an ancient hero in the Atharvaveda[9]—to which Rama, Mahavira, and the Buddha are all thought to have belonged—characterized the Kosalan realm.

[10][11] One of India's two great epics, Ramayana is set in the "Kosala-Videha" realm in which the Kosalan prince Rama marries the Videhan princess Sita.

[12] The Kosala region had three major cities, Ayodhya, Saketa and Shravasti, and a number of minor towns as Setavya, Ukattha,[13] Dandakappa, Nalakapana and Pankadha.

The Central Gangetic Plain was the earliest area for rice cultivation in South Asia, and entered the Iron Age around 700 BCE.

[22][23] The muni tradition emphasized on "practicing yoga, meditation, renunciation and wandering mendicancy" as contrasted to the ṛṣis who "recited prayers, conducted homa, and led a householder lifestyle".

[39] Shortly after the Buddha's death, the Viḍūḍabha invaded the Sakya and Koliya republics, seeking to conquer their territories because they had once been part of Kosala.

Viḍūḍabha finally triumphed over the Sakyas and Koliyas and annexed their state after a long war with massive loss of lives on both sides.

[42][43] The massive life losses incurred by Kosala during its conquest of Sakya weakened it significantly enough that it was itself was soon annexed by its eastern neighbour, the kingdom of Magadha, and Viḍūḍabha was defeated and killed by the Māgadhī king Ajātasattu.

[44] The Sohgaura copper plate inscription, probably issued during the reign of Chandragupta Maurya deals with a famine in Shravasti and the relief measures to be adopted by the officials.

[45] The Yuga Purana section of the Garga Samhita mentions about the Yavana (Indo-Greek) invasion and subsequent occupation of Saket during the reign of the last Maurya ruler Brihadratha or Pushyamitra Shunga.

[46] The names of a number of rulers of Kosala of the post-Maurya period are known from the square copper coins issued by them, mostly found at Ayodhya.

[47] The rulers, forming the Deva dynasty, are: Muladeva, Vayudeva, Vishakhadeva, Dhanadeva, Naradatta, Jyesthadatta and Shivadatta.

In this Sanskrit inscription, King Kaushikiputra Dhanadeva mentions about setting a ketana (flag-staff) in memory of his father, Phalgudeva.