Grannus was a Celtic deity of classical antiquity. He was regularly identified with Apollo as Apollo Grannus and frequently worshipped in conjunction with Sirona, and sometimes with Mars and other deities.

In Celtic polytheism, Sirona was a goddess worshipped predominantly in East Central Gaul and along the Danubian limes. A healing deity, she was associated with healing springs; her attributes were snakes and eggs. She was sometimes depicted with Apollo Grannus or Apollo Borvo. She was particularly worshipped by the Treveri in the Moselle Valley.