Stone age implements have been found near Pallavaram in Chennai. According to the Archaeological Survey of India (ASI), Pallavaram was a megalithic cultural establishment, and pre-historic communities resided in the settlement.
The region around Chennai has served as an important administrative, military, and economic centre for many centuries. During the 1st century CE, a poet and weaver named Thiruvalluvar lived in the town of Mylapore (a neighbourhood of present Chennai). From the 1st–12th century the region of present Tamil Nadu and parts of South India was ruled by the Cholas.
The Pallavas of Kanchi built the areas of Mahabalipuram and Pallavaram during the reign of Mahendravarman I. They also defeated several kingdoms including the Cheras, Cholas and Pandyas who ruled over the area before their arrival. Sculpted caves and paintings have been identified from that period. Ancient coins dating to around 500 BC have also been unearthed from the city and its surrounding areas. A portion of these findings belonged to the Vijayanagara Empire, which ruled the region during the medieval period.
The Portuguese first arrived in 1522 and built a port called São Tomé after the Christian apostle, St. Thomas, who is believed to have preached in the area between 52 and 70 CE. In 1612, the Dutch established themselves near Pulicat, north of Chennai.
On 20 August 1639 Francis Day of the East India Company along with the Nayak of Kalahasti Damarla Chennappa Nayakudu, travelled to the Chandragiri palace for an audience with the Vijayanager Emperor Peda Venkata Raya. Day was seeking to obtain a grant for land on the Coromandel coast on which the Company could build a factory and warehouse for their trading activities and was successful in obtaining the lease of a strip of land about six miles long and one mile inland in return for a yearly sum of five hundred lakh pagodas.
The region was then primarily a fishing village known as “Madraspatnam”. A year later, the Company built Fort St. George, the first major English settlement in India, which became the nucleus of the growing colonial city and urban Chennai, grew around this Fort. Post independence the fort housed the Tamil Nadu Assembly until the new Secretariat building was opened in 2010, but shortly afterwards it was again moved back to Fort St. George, due to a change in the Government.
Chennai is located on the south–eastern coast of India in the north–eastern part of Tamil Nadu on a flat coastal plain known as the Eastern Coastal Plains. Its average elevation is around 6.7 metres (22 ft),and its highest point is 60 m (200 ft). Chennai is 2,184 kilometres (1,357 mi) south of Delhi, 1,337 kilometres (831 mi) southeast of Mumbai, and 345 kilometres (214 mi) east of Bangalore by road. Two major rivers flow through Chennai, the Cooum River (or Koovam) through the centre and the Adyar River to the south. A third river, the Kortalaiyar, travels through the northern fringes of the city before draining into the Bay of Bengal, at Ennore. The estuary of this river is heavily polluted with effluents released by the industries in the region. Adyar and Cooum rivers are heavily polluted with effluents and waste from domestic and commercial sources, the Coumm being so heavily polluted it is regarded as the city’s eyesore. A protected estuary on the Adyar forms a natural habitat for several species of birds and animals. The Buckingham Canal, 4 km (2.5 mi) inland, runs parallel to the coast, linking the two rivers. The Otteri Nullah, an east–west stream, runs through north Chennai and meets the Buckingham Canal at Basin Bridge. Several lakes of varying size are located on the western fringes of the city. Some areas of the city have the problem of excess iron content in groundwater.
Chennai’s soil is mostly clay, shale and sandstone. Clay underlies most of the city, chiefly Manali, Kolathur, Maduravoyal, K. K. Nagar, Tambaram, Mudichur, Pallavaram Semmencherry, Alapakkam, Vyasarpadi and Anna Nagar. Sandy areas are found along the river banks and coasts, and include areas such as Tiruvottiyur, George Town, Madhavaram, New Washermanpet, Chepauk, Mylapore, Porur, Adyar, Besant Nagar and Uthandi. In these areas, rainwater runoff percolates quickly through the soil. Areas having hard rock surface include Guindy, Nanganallur, Pallikaranai, Alandur, Jaladampet, Velachery, Adambakkam and a part of Saidapet and Perungudi. The ground water table in Chennai is at 4-5m below ground in most of the areas, which was considerably improved and maintained through the mandatory rain water harvesting system.
Chennai is classified as being in Seismic Zone III, indicating a moderate risk of damage from earthquakes. Owing to the geotectonic zone the city falls in, the city is considered a potential geothermal energy site. The crust has granite rocks indicating volcanic activities in the past. It is expected that temperatures of around 200 to 300 C° will be available if the ground were drilled 4 to 5 km deep. The region has the oldest rocks in the country dating back to nearly a billion years.
The southern stretch of Chennai’s coast from Tiruvanmiyur to Neelangarai are favoured by the endangered Olive Ridley sea turtles to lay eggs every winter. A large number of cattle egrets, pond herons and other waterbirds can be seen in the rivers of Cooum and Adyar. About 75,000 birds migrate to Chennai every year. Marshy wetlands such as Pallikaranai also play host to a number of migratory birds during the monsoon and winter. Over 300 species of birds have been recorded in the city and its neighbourhood by members of Madras Naturalists’ Society since its inception in 1978.
Guindy National Park is a protected area within the city limits. Wildlife conservation and research activities take place at Arignar Anna Zoological Park including Olive ridley sea turtle conservation. Madras Crocodile Bank Trust is a herpetology research station, located 40 kilometres (25 mi) south of Chennai. It is India’s leading institution for herpeto faunal conservation and the first crocodile breeding centre in Asia. The city’s tree cover is estimated to be around 64.06 sq km. The most dominant tree species is the copper pod, followed by Indian beech and Neem. A total of 121 species of trees belonging to 94 genera and 42 families are found in the city.
Chennai has three rivers and many lakes spread across the city. Urbanization has led to shrinkage of water bodies and wetlands. The quantity of wetlands in the city has decreased from 650 to only 27 currently. The Chennai River Restoration trust set up by the government is working on the restoration of Adyar river. Environmentalist Foundation of India is a volunteering group working towards wildlife conservation and habitat restoration.
Chennai has a tropical wet and dry climate (Köppen: Aw). The city lies on the thermal equator and is also on the coast, which prevents extreme variation in seasonal temperature. The hottest part of the year is late May to early June, known regionally as Agni Nakshatram (“fire star”) or as Kathiri Veyyil, with maximum temperatures around 35–40 °C (95–104 °F). The coolest part of the year is January, with minimum temperatures around 19–25 °C (66–77 °F). The lowest recorded temperature was 13.9 °C (57.0 °F) on 11 December 1895 and 29 January 1905. The highest recorded temperature was 45 °C (113 °F) on 31 May 2003. The average annual rainfall is about 140 cm (55 in).
The city gets most of its seasonal rainfall from the north–east monsoon winds, from mid–October to mid–December. Cyclones in the Bay of Bengal sometimes hit the city. The highest annual rainfall recorded is 257 cm (101 in) in 2005. Prevailing winds in Chennai are usually southwesterly between April and October and north-easterly during the rest of the year. Historically, Chennai has relied on the annual rains of the monsoon season to replenish water reservoirs, as no major rivers flow through the area. Chennai has a water table at 2 metres for 60 percent of the year.