Legend has it that Appala Ranganatha was the one who led the way and measured the steps to Srirangam (Ranganatha) and thus the name ‘Kovil-Adi' (Srirangam is referred to as the ‘Kovil' among Divyadesams and ‘Adi' means ‘Step').
http://en.wikipedia.org/wiki/Appakkudathaan_Perumal_Temple
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