The reign of the Gupta Empire in Indian History is called the Golden Age of India.

The Gupta Empire ruled over a large part of northern and central India from 320 to 550 CE. During this period, India witnessed significant developments in the fields of art, literature, science, mathematics, and philosophy. The period is therefore known as the Golden Age of India.

Some of the notable achievements of the Gupta Empire are:

1. Art and Architecture: The Gupta period saw the development of the rock-cut architecture and the emergence of the temple architecture. The famous cave temples of Ajanta and Ellora were built during this period.

2. Literature: The Gupta period is considered to be the golden age of Sanskrit literature. The famous works of Kalidasa, such as Abhijnanashakuntalam, Vikramorvashiya, and Meghaduta, were written during this period.

3. Science and Mathematics: The Gupta period saw significant progress in the field of science and mathematics. Aryabhata, one of the famous mathematicians and astronomers of ancient India, lived during this period.

4. Philosophy: The Gupta period is also known for the development of various schools of philosophy, such as Vaisheshika, Nyaya, and Samkhya.

5. Trade and Commerce: The Gupta period saw an increase in trade and commerce, both within India and with other countries. The famous Silk Road that connected India with China and other countries was used extensively during this period.

In conclusion, the Gupta Empire's reign is called the Golden Age of India because of the significant progress made in various fields during this period.