 Heimdallr is attested in the "Poetic Edda", compiled in the 13th century from earlier traditional material; in the "Prose Edda" and "Heimskringla", both written in the 13th century by Snorri Sturluson; in the poetry of skalds; and on an Old Norse runic inscription found in England.Two lines of an otherwise lost poem about the god, "Heimdalargaldr", survive.Due to the problematic and enigmatic nature of these attestations, scholars have produced various theories about the nature of the god, including his apparent relation to rams, that he may be a personification of or connected to the world tree Yggdrasil, and potential Indo-European cognates.