The period assigned to Ajatshatru's rule is 491 BC to 461 BC. He was son of Bimbisara's wife Vaidehi so, the Buddhist texts mention his name as Vaidehi Putra Ajatshatru. Ajatshatru was NOT the only son of Bimbisara. There were many sons and daughters from his all wives but Ajatshatru proved to be dominant. He killed his father by starving him to death, this is what Buddhist traditions say. However, Jaina texts say that he was not involved in patricide. But, most scholars agree that he brought the life of his father to a tragic end.
The Buddhist texts related that he after starving his father to death, expressed remorse in front of Buddha, who said him, "Go and no sin more…..".
He was instigated for this crime by Devadatta. Devadatta was a distant cousin of Buddha who wanted to usurp Sangha.
The killing of Bimbisara brought enmity between Ajatshatru and Pasendi, the king of Kosala. His sister Kosaladevi died of shock of his husband's tragic end. Pasendi immediately confiscated Kashi, which was given as a gift to Kosaladevi in marriage.
Kasi a disputed territory:
Kasi remained a disputed territory between Pasendi and Ajatshatru for a long time. The dispute was solved and result was in favor of Ajatshatru, who not only absorbed Kasi to his kingdom Magadha but also got daughter of Pasendi named Vajira.
Ajatshatru expanded his territories by fighting a war with Licchhavis also. There were many reasons for his enmity towards the Licchhavis such as his half bothers were sheltered by Licchhavis, trade on the banks of river Ganga, a mine of gems near Ganga and most important the rising power of Licchhavis, which Ajatshatru wanted to destroy. The war / struggle continued for 16 years and ended in favor of Ajatshatru who absorbed the Licchhavis in his empire.
Mahshilakantaka & Rathamusala
Mahshilakantaka & Rathamusala were two war equipments used (invented) by Ajatshatru against Licchhavis. The Mahshilakantaka was an engine kind of equipment which ejected big stones. The Rathamusala was a Chariot which a musala (mace or blade) attached at both sides of chariot which when ran, caused a lot of casualties. It was also known as scythed chariot, which was invented by Ajatshatru.
During the times of Ajatshatru, both Buddha and Mahavira attained Nirvana.
Makkhali Gosala or Gosala Maskariputta, the founder of Ajivikas path also attained Nirvana during the time of Ajatshatru.
Ajatshatru and First Buddhist Council
Ajatshatru shared the relics of Buddha and enshrined them in a stupa. He also renovated 18 Buddhist Monasteries. Immediately after the death of Buddha, Ajatshatru sponsored the First Buddhist Council, which was organized in a hall erected by him outside the Sattaparnaguha Cave or Sattapani caves in Rajgir. This meeting was presided by Elder Mahakassapa. In this council Ananda recited Sutta Pitaka and Upali recited Vinaya Pitaka.
Legacy of Ajatshatru:
Ajatshatru built a fort at Pataliputra and so is known as founder of Patna. Many texts mention that is son Udayin developed Pataliputra as a city. It is said that Under Udayin Pataliputra became prosperous city which later became world's largest city under Mauryas. .