The Pallava empire, although having had been the first multi-cultural empire of Tamilnadu, ceased to exist during this time line. However, Parthibendra Pallava is addressed as a king here. He could have been a subsidiary king though, as in history many with the name "Pallavarayan" continued to serve as head generals in the Chozha army.
The Marwari breed of horses were used for shooting this film. A horse had died in shooting too. In history though, the fastest horses in the world were imported from Arabia for warfare in the Chozha cavalry.
The last Pandyan emperor was indeed assassinated by his own son, in the battle between his sons for the throne, as another son was chosen for the succession. This is referenced by Nandini as a possible scenario, four hundred years before this happened. Never have in Tamil history has such a thing happened and Nandini's words were not to be taken so seriously as in the film.
Thailand was the location for all Lanka scenes in the film, understandably due to the civil war era sensitivity in Sri Lanka. However, even the first shot of Cauvery River were shot in Andhra/Telengana which do not have the titular river..