Treta Yuga (Devanagari: त्रेता युग) is the second out of four yugas, or ages of mankind, in the religion of Hinduism, and follows the Satya Yuga of perfect morality and precedes the Dvapara Yuga. The most famous events in this yuga were Lord Vishnu's fifth, sixth and seventh incarnations as Vamana Parashurama and Ramachandra respectively. The Dharma bull, which symbolises morality, stood on three legs during this period. It had all four in the Satya Yuga and two in the later Dvapara Yuga. Currently, in the immoral age of Kali, it stands on one leg. The average lifespan of the Treta Yuga is 1,296,000 years.
Avatars of Vishnu during Treta Yuga
Vishnu incarnated as the dwarf son of Aditi to stop King Mahabali of the Asura race, the grandson of Prahlada, from completing a sacrifice which would allow him to overshadow Indra in power and splendor. The jealous and worried Devas persuaded Vishnu to send Bali, a bhakta of his, to Patala, the underworld. Vishnu did so by taking advantage of the King's kindness and refusal to go back on his word, but allowed him a luxurious dwelling and sovereignty in one of the lower worlds. He also gave him the boon of being able to visit his subjects once every year which is celebrated in onam festival.
Vishnu incarnated as the Brahmana Parashurama in this era because there were too many warlike kshatriyas plaguing the Earth, and he therefore had to wipe out most of the world's warriors. However, some of the Kshatriyas survived or more were created, and their population grew again. Eventually, the avatara of Vishnu in Parashurama ended, though it is said that he continued to live on as a mighty warrior-hermit. He confronted Ramachandra angrily years later, before acknowledging the latter's supremacy and retiring. He lived on in the Dvapara Yuga, having a great duel with Bhishma for Amba's sake (and losing), and he taught Karna how to use the Brahmastra and cursed him when he found out that he was not a Brahmin but a kshatriya. He had vowed not to teach or be a Guru of Kshatriyas. He is said to be still alive today, meditating on Mahendra mountain or deep in a forest.
The hallmark of this era was the rise of evil in the form of the demon king of Lanka, Ravana. He conquered the three worlds namely, earth, heavens and the netherworlds (patala) and terrorized everyone. Even the Devas were subordinate to him - his son Meghanada had earned the name of Indrajit by defeating Indra, the King of heaven, in battle; and even the Sun had to obey the rakshasa king. In this scenario, Lord Vishnu incarnated himself as the son of King Dasaratha of the Sun Dynasty or Ikshvaku dynasty and was named Lord Rama. Due to a stepmother's jealousy, Lord Rama was sent away to the forest in exile for 14 years, during which time he confronted and killed Ravana for having kidnapped his wife, and thus restored peace on earth. He is said to have afterwards ruled the Kingdom of Kosala from Ayodhya for an eleven-thousand year golden age known as the Rama-rajya or Rama's Kingdom, before eventually returning to his Mahavishnu form with his three half-brothers- Lakshmana, Bharata and Shatrughna- who were "minor" incarnations of Vishnu or the great serpent-gods Shesha.