Books are the carriers of civilization. They are companions, teachers, magicans, banker's of the treasures of the mind. Sir... Congratulations for the book of "Yakkshi".
According to a narrative in wikipedia there had been a tussel for the rule between two groups, one having lineage to Mourya and the other, belonging to lamba karnas around 7th century. Perhaps the former left for the area known as Sri Vijaya (in Sumathra) which perhaps sprung up around that time. They may have left the east of our country leaving all those creations that are now in the jungles. I have met youths from that region who are proud to say they belong to Sri Vijaya. And they were Buddhist. There are monumants named as 'kotha'.
It should be relatively easy to work out whether a sophisticated culture existed in Sumatra 1200 or so years ago. Isn't it? On the other hand, what about the Angkor-what civilization, which did exist from 9th century onwards for 600 years. And they were indeed warring and also highly successful. Also with Indian origin. Just a thought.
The 'govi' in nissanka malla inscriptions are 'kilingu' caste people to which his predecessor (mahinda vi) belonged. govigama is a colonial caste. A mix of colonial bootlickers from low country and Malabar vellalas from up country.