Nilavarai is a hidden place - forbidden for common people. Doubt inscriptional support for this.
However, The famous Nallur Nataraja bronze was found from the Nilavarai of Nallu (during Dr. Nagaswamy's tenure).
About 20 years back, from Esalam, several Bronze were found in the Nilavarai of Esalam Eswara Temple. Sadasiva Batta was the main priest in whose favour, Rajendra has constructed this temple.
Like Forts & Agazhis, Nilavarai was also part of special type constuction.
Ancient Tamil Kings were good in infrastructure developments.
There were SEPARATE ROADS for TRANSPORTING HEAVY GOODS ! Imaging transporting NANDHIs in the finished form to Thanjai - from the origin of Pachamalai (near Narthamalai / Karur or so ..).
They used SAGADA PERUVAZHI for transporting heavy materials .. Nila Vazhi :: Rajapattai - Peruvazhi (Highway) - Sagada peruvazhi Neer Vazhi :: Boating etc. In the Sea, using Ships;
Their engineering was marvellous. You will realise in ?Thanjavur.