Cycle of Four Ages – The belief that time is a cycle made up of four ages, and that the cycle repeats itself endlessly

To remember the meaning of the Hindu term Cycle of Four Ages, use the following mnemonic:

They had to cycle for ages (cycle of four ages) – the journey seemed to repeat itself endlessly.

According to Hindu beliefs, the process of creation moves in cycles and each cycle has four great yugas, or epochs, of time. Because the process of creation is cyclical and never-ending, Hindus say it "begins to end and ends to begin."​

A Kalpa, or eon, comprises a thousand cycles of four yugas, each of a different quality. A single yuga cycle is said to be 4.32 million years, and a Kalpa 4.32 billion years

The four great epochs in Hinduism are Satya Yuga, Treta Yuga, Dwapar Yuga, and Kali Yuga. Satya Yuga, known as the Age of Truth, is said to last for 4,000 divine years (a divine year equals 432,000 earthly years). Treta Yuga lasts for 3,000 years, Dwapara Yuga for 2,000 and Kali Yuga, 1,000 divine years. 

Hindus believe that, for the current universe, three of these great ages have already passed and we are now living in the fourth one – the Kali Yuga.

The numbers involved are so huge, it is difficult to contemplate the meaning of the vast quantities of time involved. There are also many different theories about the symbolic meanings of these measurements of time.