Alwars, who are said to be the Hamsam (form) of Sriman Narayanan, have sung Mangalasasanam (praising of the Perumal) on the Perumal and there are totally 108 Sthalams where Alwars have done Mangalasasanam on the Perumal. These 108 Vishnu Sthalams are called as "Divyadesams".