The temple complex was built on the banks of the river cauvery, with its water diverted to the moat. The walls around the temple was constructed in the form of fortress, to protect the temple from invaders. Even today the temple has one of the highest gopuram ( 66 meters – 216 feet ) in India. The Kalash ( shikara ) which is installed on top of the Vimana weighs a massive 81.5 tonnes. A ramp was constructed from 6 kms away from the temple complex to roll over the huge shikara on to the gopuram. The entire temple is built with granite which was not available in the area. Probably it was transported from Trichy Rockfort area which is located 40 kms away. The inspiration to create the magnificient edifice seems to have been inspired by the Chalukyan architecture. The gurus advice to atone for the sins in the form of bloodshed of his rivals to the throne, by building an edifice to Lord Shiva.

Representative of Craftsmanship
The details of the stone work of this imposing vimanam are representative of the masterly craftsmanship of South Indian artisans. The shilpi [sculptor] and the sthapathi [architect] came together to create their fanciful abode for Shiva. Naturally, the shape had to echo Mount Kailash itself. In its perfect geometry and distinct clarity of lines, this tower is unbeatable.

The Srivimanama, or tower over the main shrine, of the Brihadeswarar temple is 61 metres tall. Imagine that being built in 1002 CE. The foundations for it are only 2 metres deep - it is constructed in such a way that the weight of the Vimanam is evenly distributed on itself. It is hollow inside and layered to allow access for the intrepid.
The top the pyramid-shaped tower holds the Vimana - a monolithic huge rock spherical in shape, weighing approximately 81 tones. Above the Vimana the Kalasam made up of gold can just be seen - its height is 4m and it was originally presented by Rajaraja Chola 1. 
On the flat roofed portions of the structure, you can see many Nandi statues. Each of the 16 or so layers of the tower contain intricate carvings. If you view this pic large (see link below), you can view some of them on the lower layers.

Every feature of the temple is larger than life — the monolithic Nandi, the gigantic [12-feet high] Dwarapalakas [guardian deities] and the sculptures in the niches around the central shrine. They are distinguished by an elegant simplicity in lines and ornamentation. The faces of the figures like Dakshinamurthi and Yogalakshmi are beatitude in essence. Inside the vimanam, there is a hidden corridor surrounding the sanctum. Rarely open to visitors, this is a treasure trove of Chola painting and sculpture. The walls of this cave-like corridor were plastered with lime and used as a large canvas for the paintings. Perhaps the subjects chosen were dear to the great king's heart, for, he was a staunch Shaivite, a great warrior who took pride in his victories, and was responsible for the renaissance of the Bhakti movement through the spread of the songs of the saints ( Thevaram). The paintings, which have survived time and a 17th century coat of paint, are exquisite in detail and colour, and proportion. The colours in the paintings are subdued, the lines are delicate and the expressions vivid and true to life. 

Figures of Dakshinamurthi, Nataraja in Thillai, surrounded by celestials, dancers and saints in a celebration, and Tripuranthaka, the gigantic warrior, are masterpieces of Chola painting. The story of Sundaramurthi Nayanar reaching Kailash on a white elephant is depicted on another wall. 

The most telling of all is the portraiture of Raja Raja with his Guru Karuvur Devar. It was Karuvur Devar, the administrator, whomaster-minded the building of the temple, and fittingly he has a special shrine dedicated to him in the outer courtyard of the temple. While the sculptures of Shiva in this corridor are imposing and colossal, the fine series of 81 karanas (dance poses) are superb illustrations of the Natya Sastra. These figures are much bigger than the dance figures in Chidambaram and other temples.

The Architectural Beauty

Little is known as to who designed the Big Temple but it succeeds in projecting the grand imperial vision of a king who expanded theboundaries of the Chola empire. 

In 1946, after Archaeological Survey of India (ASI) took charge of the conservation of Brahadeeswara temple at Thanjavur, conservationists noticed that the jambs and lintels of all the doorways in the tower were systematically damaged by gun fire [caused in the 19 century]. The intent behind this wanton destruction, the conservationists observed, “was perhaps to let the whole structure collapse by itself”.

None of that happened. Good design and sound structural logicserved in good stead and for the last thousand years the structure has stood firm. The Brahadeeswara temple, completed in 1010 CE, for good reasons, is celebrated as a towering example of architectural excellence.

A monument was in order after Rajaraja I (985-1014), the Chola emperor, had vastly expanded the limits of the empire and brought immense wealth. It had to be ambitious and befit the imperial vision. By that time, temple architecture in South India had significantly advanced. The Pallavas of Kanchipuarm, in the 8th century, demonstrated how multilevel functional temples could be built. There were also examples of temples with more than three tiers. These structures offered a broad template, but it was clear to the architects of Rajaraja that the temple at Thanjavur should far exceed all of them.

Rajarajesvaram, as the temple complex was known in theinscriptions, when completed, was 40 times larger and five times taller than any average temple that preceded it and consumed130,000 tons of graniteThe 60-metre tall vimana[tower over the sanctum] built in 15 tiers, appeared like a huge mountain and remains the tallest in South India.

The unusually tall vimana alone weighed about 43,000 tons and supporting it was a challenge. Though the pyramidical shape of the vimana is self-stabilising, the architects could not afford to make the base appear wide and loose out on the visual appeal.

A proportionately large sanctum with double walls and circumambulatory passage in-between was designed. It rose to two tiers and merged at the third and held the tower.

Simultaneously, the vimana and the structures in front were consciously separated by a constriction in the elevation so that the tower could visually stand out.

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