Thrissur has a rich history dating back to ancient times, and is known for its cultural and religious significance. 

The earliest recorded history of Thrissur dates back to the 9th century, when it was known as "Vrishabhachalam". It was a center of Hinduism and Buddhism during this time. In the 14th century, the city came under the rule of the Zamorin of Calicut, who was a powerful ruler in the region. 

In the 16th century, Thrissur came under the control of the Cochin Kingdom, which was ruled by the Portuguese. The city grew in importance as a center of trade and commerce during this time, and many European traders and merchants settled in the area. 

During the 18th and 19th centuries, Thrissur became a center of resistance against British colonialism. Many notable freedom fighters and leaders were born or lived in the city during this time, including Raja Ravi Varma, who was a renowned painter and artist. 

In the 20th century, Thrissur became a major cultural center in Kerala, with a thriving film industry and a rich tradition of music, dance, and theater. The city is known for its colorful festivals, including the world-famous Thrissur Pooram, which is celebrated in April or May each year.