The earliest inscriptions to refer Kollavarsham (the Malayalam era) are the Mamballi plates discovered from the Mamballi Madhom at Keezhattingal near Attingal. The copper plates are named after the Mamballi Madhom from where they were discovered.
The plates have the earliest reference on the Panankavu Palace of the Venad rulers.
The Venad kings mentioned in all the inscriptions, except the Tharisapalli plates, is Sreevallabhan Kotha. Ayyanadikal Thiruvadikal is the Venad ruler mentioned in the Tharisapalli plates.
The notable portion in the Mamballi plates is one describing a meeting attended by Venad ruler Sreevallabhan Kotha, Adichan Umayamma of Thirukkalayapuram, members of the Chengannur temple administration committee including one Poduval at the Panammavil palace in Kollam.
The meeting finalised the administrative rules for the Ayiroor temple and Chittoor Nada. The plates also say about a man who donated land to the Chengannur temple.
The inscriptions that date back to AD 974 reveal some historic incidents of that period. They helped historians to determine the period of Kulasekhara rulers Bhaskararavi and Indukothavarma.
Though some claim that the inscriptions are in Tamil, they were disproved by historians citing the words "vechu", "rakshichu", "paduvithu", "irunnaruliyedathu" and "attiyeduthu" - all non-Tamil.