Kosala (Sanskrit: कोसल) was an ancient Indian region, corresponding roughly in area with the region of Awadh in present day Uttar Pradesh. According to the Buddhist text Anguttara Nikaya and the Jaina text, the Bhagavati Sutra, Kosala was one of the Solasa (sixteen) Mahajanapadas (powerful realms) in 6th century BCE and its cultural and political strength earned it the status of great power. However, it was later weakened by a series of wars with the neighbouring kingdom of Magadha and, in the 4th century BCE, was finally absorbed by it. The Kosala region had three major cities, Ayodhya, Saket and Shravasti and a number of minor towns as Setavya, Ukattha, Dandakappa, Nalakapana and Pankadha. According to the Puranas, Ayodhya was the capital of Kosala during the reign of Ikshvaku and his descendants. Shravasti was the capital of Kosala between 6th century BCE and 6th century CE.
The mention of Kosala is not found in the early Vedic literature. It is mentioned as a region in the later texts of the Satapatha Brahmana and the Kalpasutras.
In the Ramayana, Mahabharata and the Puranas the ruling family of the Kosala kingdom was descended from king Ikshvaku. The Puranas give lists of kings of the Aikhsvaka dynasty (the dynasty founded by Ikshvaku) from Ikshvaku to Presenajit (Pasenadi). A Buddhist text, the Majjhima Nikaya mentions Buddha as a Kosala'n and Mahavira, the 24th Tirthankara of Jainism taught in Kosala. In the time of king Mahakosala, Kashi was an integral part of the kingdom. Mahakosala was succeeded by his son Pasenadi (Prasenajit). He was a follower of Buddha. During his absence from the capital, his minister Digha Charayana raised his son Vidudabha to the throne. Kosala kingdom was absorbed not much later into Magadha kingdom.
Kosala under Mauryan rule
It is assumed that during the Mauryan reign, Kosala was administratively under the viceroy at Kaushambi 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. The Yuga Purana section of the Gargi Samhita mentions about the Yavana (Indo-Greek) invasion and subsequent occupation of Saket during the reign of the last Maurya ruler Brihadratha.
Kosala in post-Mauryan period
The names of a number of rulers of Kosala of the post-Maurya period are known from the square copper coins issued by them. The rulers are: Muladeva, Vayudeva, Vishakhadeva, Dhanadeva, Naradatta, Jyesthadatta and Shivadatta. There is no way to know whether king Muladeva of the coins is identifiable with Muladeva, murderer of the Sunga ruler Vasumitra or not (though a historian, Jagannath has tried to do so). King Dhanadeva of the coins is identified with king Dhanadeva (1st century BCE) of Ayodhya inscription. In this Sanskrit inscription, King Kaushikiputra Dhanadeva mentions about setting a ketana (flag-staff) in memory of his father, Phalgudeva. In this inscription he claimed himself as the sixth in descent from Pusyamitra Sunga. Dhanadeva issued both cast and die-struck coins and both the types have a bull on obverse.