Periyar (meaning: big river) is a river flowing in the state Tamilnadu & Kerala, India, with a length of 244 km in Kerala. It is one of the few perennial rivers in the region and provides drinking water for several major towns. The Idukki Dam on the Periyar generates a significant proportion of Kerala's electrical power.

It originates from the Sivagiri peaks (1800m MSL) of Sundaramala in Tamil Nadu. The total length is about 244 km with a catchment area of 5,398 km² (5,284 km². in Kerala, 114 km². in Tamil Nadu). It flows northwards for 48 km and at Thekkady joins the west-flowing Mullayar, which is a tributary of the periyar. The Mullaperiyar dam is constructed at the confluence of both the rivers Periyar and Mullayar to create the Periyar lake and reservoir and the Periyar National Park.

From Periyar Thekkady lake and reservoir, water is diverted eastwards to Tamil Nadu via a tunnel enabling the water to join the Vaigai River. From Periyar Thekkady Reservoir, the Periyar river flows northwestward for 35 km through Vandiperiyar, Elappara and Aiyyappankoil to join the Idukki reservoir formed by the Idukki, Cheruthoni and Kulamavu dams. From Idukki reservoir, Periyar river flows northwestwards and then westward to join the Arabian sea at Munambam near Kodungallur and the Vembanad lake at Kochi.

Adi Shankara (Sanskrit: आदिशङ्करः Ādi Śaṅkara, pronounced [aːd̪i ɕəŋkəɾə]) (788 CE - 820 CE), also known as Śaṅkara Bhagavatpādācārya and Ādi Śaṅkarācārya was an Indian sage from Kalady in present day Kerala who consolidated the doctrine of advaita vedānta. His teachings are based on the unity of the ātman and brahman— non-dual brahman, in which brahman is viewed as nirguna brahman, brahman without attributes.

Shankara travelled across the Indian subcontinent to propagate his philosophy through discourses and debates with other thinkers. He is reputed to have founded four mathas ("monasteries"), which helped in the historical development, revival and spread of Advaita Vedanta of which he is known as the greatest revivalist. Adi Shankara is believed to be the organizer of the Dashanami monastic order and the founder of the Shanmata tradition of worship.

His works in Sanskrit concern themselves with establishing the doctrine of advaita (nondualism). He also established the importance of monastic life as sanctioned in the Upanishads and Brahma Sutra, in a time when the Mimamsa school established strict ritualism and ridiculed monasticism. Shankara represented his works as elaborating on ideas found in the Upanishads, and he wrote copious commentaries on the Vedic canon (Brahma Sutra, principal upanishads and Bhagavad Gita) in support of his thesis. The main opponent in his work is the Mimamsa school of thought, though he also offers arguments against the views of some other schools like Samkhya and certain schools of Buddhism.