Kāla Cakra

One full turn has two halves. Avasarpiṇī descends: everything good diminishes. Utsarpiṇī ascends: everything good returns. Each half has six spokes, called aras, and each half lasts ten crore-crore sāgaropama.

In the descending half, lifespan, height, strength, stature of grain, and even the potency of the earth fall step by step. In the ascending half they climb back. Nothing is lost permanently and nothing is gained permanently. There is no progress and no fall — only a wheel.

Twenty-four Tīrthaṅkaras appear in each half. In our descending half the first was Ṛṣabhanātha and the twenty-fourth was Mahāvīra, who reached liberation three years and eight and a half months before this ara began.

We are in the fifth ara of an avasarpiṇī: Duḥṣamā, the unhappy age. It lasts 21,000 years, of which about 2,500 have passed. After it comes Duḥṣamā-duḥṣamā, worse again, and after that the wheel turns and the ascent begins.

None of this happens in Mahāvideha Kṣetra, which stays permanently as the fourth ara. That is the whole reason Mahāvideha matters.