Pre-history
The Ramavarmapuram monument is in granite and is of the menhir type. The monument in Ramavarmapuram is 15 feet (4.6 m) in height and 12 feet 4 inches (3.76 m) wide. Since 1944, it has been protected by the Department of Archaeology. The monument is locally known as Padakkallu or Pulachikkallu. These menhirs are memorials put up at burial sites for the departed souls. They belong to the Megalithic Age of Kerala, which is roughly estimated between 1000 BCE and 500 CE. All such monuments have not been dated exactly. Some experts are of the view that these are the remnants of the Neolithic Age in the development of human technology. The Ramavarmapuram menhir is also believed to be a monument belonging to the Sangam period in the South Indian history.

Another monolithic monuments like Dolmens and rock-cut caves are at Porkulam, Chiramanengad, Eyyal, Kattakambal and Kakkad. According to historians, the dolmens are burial sites. Though most of the monuments were well protected, the dolmen at Porkulam was in a neglected condition. The monument excavated under eminent Archaeologist B. K. Thapar, between 1949 and 1950, was under the Department of Archaeology. Another megalithic monument is situated at Ariyannur in Thrissur. This place has unravelled monuments such as the Kudakkallu or Thoppikkallu (Mushroom stones or Umbrella stones) and 'Munimada' (Saint's abode).The laterite hillocks of Ariyannur rise to about 50 metres. Another reference in Ariyannur dates back to the early 15th century in the poem Chandrotsavam.

Pre-colonial history
The region can claim to have played a significant part in fostering the trade relations between Kerala and the outside world in the ancient and medieval period. The early political history of Thrissur is interlinked with that of the Chera Dynasty of the Sangam age, who ruled over vast portions of Kerala and Tamil Nadu. After the Cheras, the place was later ruled by the Kingdom of Cochin (Perumpadapu Swaroopam). Later, a powerful dynasty known as Zamorins of Calicut captured most of the Thrissur in 14th and 15th century.

Colonial period
Next was the turn of Portuguese who ruled Thrissur in the 16th century. In the beginning of the 17th century the Portuguese power was reduced and Dutch became the main power. With the help of Dutch, Cochin Royal Family recaptured Thrissur from Samoothiri in 1710.

The modern City of Thrissur rose to importance after Sakthan Thampuran ascended the throne of Kingdom of Cochin (1769–1805). He changed the capital of Cochin Royal Family to Thrissur from Mattancherry and abolished the power of Namboothiri community, which controlled most of the temples of Thrissur district. The maharaja destroyed the forest around the Thekkinkadu Maidan which seats the Vadakkumnathan temple, and started the most spectacular cultural festival called Thrissur Pooram. Sakthan Thampuran laid the modern foundation stone of Thrissur and made the city into a major financial and commercial hub of South India, by inviting Syrian Christian families and Brahmins from adjoining areas.

However, during 1750–60 Hyder Ali, the Sultan of the powerful Kingdom of Mysore, conquered Thrissur and Thrissur became tributary of the Kingdom of Mysore. Tipu Sultan, his son led another invasion in 1786 to Thrissur. Later he made a retreat from Thrissur, which served as the headquarters of the Kerala region, after the Srirangapattanam war. In the meantime, Rama Varma X, the successor of Sakthan Thampuran signed a treaty with East Indian Company, and made Cochin a subsidiary of the British.

Anti-Colonial movements
The Indian freedom movement struggle also grew in momentum in Thrissur after a Committee was formed in 1919 of the Indian National Congress. In 1921, the Civil Disobedience Movement also attracted a large number of people into the freedom struggle. In 1927 Mahatma Gandhi visited Vivekodayam School in the city. In 1934, father of the nation, again visited the city for the housewarming of Barrister Krishna Menon. The house afterwards was known "Gandhi Mandiram" in Chembukkavu. In the meantime, R. K. Shanmukham Chetty, the controversial Diwan of Cochin Kingdom from 1935 to 1941, developed the city by constructing Thrissur Town Hall and Ramanilayam. Even now these two buildings remain important in Kerala politics. Dr. M. R. Menon, a minister in Government of Kochi was instrumental in building the Municipal Corporation Building, Thrissur and the Municipal Office Road. He concreted Swaraj Round and other peripheral roads of the city.

Post-Colonial
In 1947, when India gained independence from the British rule, Thrissur was under Kingdom of Cochin. Thrissur district was formed on 1 July 1949, with the headquarters at Thrissur City. The city is usually referred to as the Cultural Capital of Kerala. The city had been home to politicians and bureaucrats like R. K. Shanmukham Chetty, P.C. Rao, C. Achutha Menon, K. Karunakaran, Joseph Mundassery, Vinod Rai etc. after the independence. These individuals have changed the trajectory of Thrissur City afterwards.

P.S. Rao, advisor to the Rajapramukh and acting Governor of Kerala, is another person who Thrissukkar is indebted to. He expanded Thrissur City by shifting all the administrative and government offices like Thrissur Collectorate to Ayyanthole from Chembukavu. Government Engineering College, Thrissur, is another gift from Joseph Mundassery, the controversial former education minister who introduced Kerala Education Act. C. Achutha Menon, the former Chief Minister of Kerala gifted Kerala Agricultural University in 1971, a university for all agricultural related activities.

K. Karunakaran, the Bhishma of Kerala politics started his career in Thrissur as a painter. Later on he became the "Leader" of city. During his regime Thrissur-Guruvayur Section and Poonkunnam Over Bridge was built. Vinod Rai, the Comptroller and Auditor General of India, is another person who turned fortunes of the city by building Sakthan Thampuran Nagar (S.T.Nagar) when he was collector of Thrissur district. He is also known as the second Sakthan Thampuran of Thrissur by shifting the Municipal Stand near the M.O. Road to Shaktan Thampuran Nagar, now known as Shaktan Thampuran Private Bus Stand, Thrissur. Another IAS officer who made remarkable contributions to the development of Trichur is Raju Narayana Swamy. He single-handedly widened five roads of the city- Pattalom Road, Inner Ring Road, Ragam Theatre Road, Padinjare Kotta and Chemputti Lane – thereby changing the face of the town.

The city of Thrissur is situated in Thrissur District of Central Kerala in India. The city is located at 10.52°N 76.21°E and has an average altitude of 2.83 metres. The city is 75 km north-east of Kochi, 133 km south-west of Coimbatore , 124 km south-east of Kozhikode and 151 km north of Changanacherry. The city is located in a hillock called Thekkinkadu Maidan which is the second highest point in city after the Vilangan Hills. From the hillock, the geography of the city move towards middle land where Thrissur Kole Wetlands is situated. The Kole Wetlands act as a natural drainage for the city where the water is carried out to river and from there to the Laccadive Sea, thus keeping Thrissur city safe from flood waters which affect most of the other cities in Kerala. Different ponds, rivers and canals also keep the ground water safe from salt waters. The city is located in midland regions of Kerala, with an extended part of Palakkad plains. The city geologically is composed of Archaean gneisses and crystalline schists. Major parts of city is covered by Archaeans rocks. The city lies near the centre of the Indian tectonic plate (the Indian Plate) and is subject to comparatively little seismic or volcanic activity.