Theory:

Poompuhar is once the ancient capital of the Chola dynasty. The earliest reference of Puhar can be found in the old Sangam era epics as well as in the Periplus of the Erythraean SeaKovalan, Kannagi and Mathavi of Tamil epic 'Silapathikaram' lived here.
 
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Kannagi statue in Poompuhar.
 
Present Poompuhar has the memorial story of the epic in small sculptures. It has a beautiful beach, a lighthouse, a Maritime museum and Kannagi temple.
 
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Natural and Ancient beach located at Poompuhar.
 
Poompuhar is situated on the bank of the river Cauvery. One can able to witness the incredible experience of the river Cauvery flowing into the sea here.
 
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Kaveri Sangamam - Poompuhar
 
Poompuhar is a major port city of the early Chola kingdom on the mouth of the Cauvery river. The place where the river meets the Bay of Bengal, it was known by various names such as Puhar, Poompuhar, Kaveripoompattinam, and Kaveripattinam through time.
 
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Map showing the path of river Cauvery (Kaveri) joining the
sea at Poompuhar.
Reference:
1. https://commons.wikimedia.org/wiki/File:Kannagi_statue_in_Poompuhar_1_JEG6142.jpg
2. https://www.flickr.com/photos/ravages/3151039468/in/photostream/
3. https://commons.wikimedia.org/wiki/File:River_Cauvery_EN.png