Winterfylleth is an English black metal band from Manchester. Since their inception in 2006, the band has released seven studio albums and have become a popular act in both the English underground metal scene and the wider international metal arena. Winterfylleth are self-described as "English Heritage Black Metal" and is often considered to be musical 'brothers-in-arms' with fellow English black metal band Wodensthrone owing to the common lyrical and aesthetic themes they share. The band takes its name from the Old English word 'Winterfylleth', which translates into modern English as 'Winter Full Moon' and is signified by the arrival of the first full moon of winter.

The Mercian Sphere is the second studio album by the English black metal band Winterfylleth, released on 12 July 2010 through Candlelight Records. It was made after Winterfylleth regrouped in 2009 and was the band's first collaboration with Candlelight Records. It contains Anglo-Saxon lyrical subjects and influences from folk music.