Most of what we know of the early Cholas is found in the Tamil Sangam literature, secular writings from southern India composed between 200 BCE and 500 CE. There are legends about mythical Chola kings who were said to be descended from the sun. One of these mythical kings, Kantaman, was even credited with creating the river Kaveri through his great devotion. In later centuries, these early connections were important to the rulers because they established an hereditary right to the kingship.

The Cholas are mentioned in the Periplus of the Erythraean Sea, a navigation and commerce manual written by an anonymous first century Alexandrian Greek, which describes an active trade between the Cholas and the Romans. Ptolemy's second century Geography adds further details to our knowledge of the Cholas. The Cholas are noted in the Buddhist historical record, the Mahavamsa, and the name was inscribed upon the Pillars of Ashoka, a series of columns erected in northern Indian by the Mauryan emperor Ashoka during the third century BCE.

The Sangam literature describes the Kaveri River basin as a fertile land where everyone had plenty to eat. The monarchy was hereditary, though the succession was often disputed to the point of civil war. Laws were primarily those of custom rather than writ, and the king himself meted out justice to all levels of society.

During the first and second centuries CE, there were three ruling families in southern India, the Pandyas, the Cheras, and the dominant Cholas. After the third century, a non-Tamil Buddhist clan of uncertain origin called the Kalabharas overran southern India. The Cholas fell into obscurity until Vijayalaya Chola captured Thanjavur and founded a new line of Chola kings around 850.


sources:
Wikipedia - Chola Dynasty
Hindunet