Legends sanctified Ujjain as the “seed city”. It is believed that the germs of all living beings who survived the Flood are preserved in the central image of Mahadeo in the great Mahakal temple. Sanctity is attached to birds and beast and fish and all living creatures.

Maha Kaal means both ‘the death of death’ and ‘time’ also meaning ‘immortality’ and ‘infinity’. Lord Shiva graciously agreed to abide forever in Ujjain in his form as Mahakaleshwar, the Lord of Eternity.

Thus, he became a marvellous pillar of light, a Jyotirling. A naturally-manifested stone lingam represents this even today.

Maha Shivaratri is a big event here. Thousands of pilgrims flock to the fair grounds near the Mahakal temple to worship Lord Shiva. The Simhastha Kumbh Mela is a mammoth fair held once in twelve years.

The city is also sacred because Sri Vallabhacharya, a Vaishnava reformer took abode under a pipal tree here.

The Ujjain panchangam or lunar calendar is still calculated here and followed by millions.

Source: https://utsav.gov.in/view-darshan/shree-mahakaleshwar-temple-live-darshan-1