The Mauryan art is believed to be inspired from Achaemenid or Persian influence. We can find a lot of similarities in terms of form and style in the inscriptions of Ashoka and the Persian king Darius.
Lion was one of the motifs used in Ashokan pillars. Lion is a solar symbol and it also represents the Buddha, as he is referred to as Sakyasimha which also means a lion among the Sakyas.