Complex sentence: Later, in 757, the Royal Frankish Annals state that Tassilo became Pepin's vassal for his lands at an assembly held at Compiegne, where he is reported to have sworn numerable oaths to Pepin and promised fealty to King Pepin and his sons Charles and Carloman.
Split into simpler sentences: Later, in 757, according to the Royal Frankish Annals, Tassilo became Pepin's vassal for his lands at an assembly held at Compiègne. There he is reported to have sworn numerous oaths to Pepin and promised fealty to him and his sons, Charles and Carloman.