Complex sentence: Alexius set out to reform the church institution of the "charistike dorea" (donation), which recent research dates to the period just after the Triumph of Orthodoxy (843).
Split into simpler sentences: Alexius set out to reform the church institution of the "charistike". The institution of the "charistike dorea" (donation), which recent research dates to the period just after the Triumph of Orthodoxy (843).