Mahabalipuram is a temple town situated along the shores of the Bay of Bengal about 60 kms from the south Indian city of Chennai.  The town is famous for its stone carvings made during the Pallava dynasty in 7th – 9th century.  These structures are massive and beautiful.

This group of sanctuaries, carved out of rock along is known especially for its rathas (temples in the form of chariots), mandapas (cave sanctuaries), giant open-air reliefs such as the famous ‘Descent of the Ganges’, and the temple of Rivage, with thousands of sculptures to the glory of Shiva.

Founded in the 7th century by the Pallavas sovereigns south of Madras, the harbour of Mahabalipuram traded with the distant kingdoms of southeast Asia : Kambuja (Cambodia), Shri vijaya (Malaysia, Sumatra, Java) and with the empire of Champa (Annam). But the fame of its role as a harbour has been transferred to its rock sanctuaries and Brahmin temples which were constructed. or decorated at Mahabalipuram between 630 and 728. These monuments may be subdivided in five categories:

• the ratha temples:in the form of processional chariots, monolithic constructions cut into the residual blocks of diorite which emerge from the sand. The five ratha of the south, which are the most famous, date to the reign of Narasimhavarman Mamalla (630-668), the great Pallavas king (the Cholas texts, moreover, call the city Mamallapuram)
• the mandapa , or rock sanctuariesmodeled as rooms covered with bas-reliefs (the mandapa of Varaha, representing the acts of this avatar of Vishnu; the mandapa of the five Pandavas and, especially, the mandapa of Krishna and the mandapa of Mahishasuramardini)
• the rock reliefsin open air, the largest of which is world renowned, illustrates a Popular episode in the iconography of Siva, that of the Descent of the Ganges:  the wise King Baghirata having begged him to do so, Siva ordered the Ganges to descend to earth and to nourish the world. The sculptors used the natural fissure which divided the cliff to forcefully suggest this cosmic event to which a swanning crowd of gods, goddesses, mythical beings (Kinnara, Gandherva, Apsara, Gana, Naga and Nagini), savage and domestic animals bear witness.
• temples, constructed in cut stone, like the temple of Rivage, which was constructed under the King Rajasimha Narasirnhavarman II (695-722), with its high stepped pyramidal tower and thousands of sculptures dedicated to the glory of Siva.

Criterion (i): the bas-relief of the “Descent of the Ganges” is -like that of the island of Elephanta- a unique artistic achievement.

Criterion (ii): the influence of the sculptures of Mahabalipurarn, characterized by the softness and suppleness of their Modeling, spread afar (Cambodia, Annarn, Java)

Criterion (iii): Mahabalipurarn is, pre-eminently, the testimony to the Pallavas civilization of southeast India

Criterion (vi): the sanctuary is one of the major centres of the cult of Siva.

Source:

http://whc.unesco.org/en/list/249/documents/

http://www.indiamarks.com/the-monuments-mahabalipuram/

https://en.wikipedia.org/wiki/Group_of_Monuments_at_Mahabalipuram