Complex sentence: In 925 Æthelstan behaved as a Mercian king, describing himself as "Rex Anglorum" in a charter relating to land in Derbyshire, witnessed only by Mercian bishops.
Split into simpler sentences: In 925 Æthelstan behaved as a Mercian king. In a charter of that year relating to land in Derbyshire he described himself as "Rex Anglorum", and it was only witnessed by Mercian bishops.