Complex sentence: In discussing the "shuyuan", it is common to speak of the "Four Great Academies" (四大书院) of ancient China, generally referring to the four major academies of the Northern Song.
Split into simpler sentences: In discussing the "shuyuan", it is common to speak of the "Four Great Academies" (四大书院) of ancient China. Usually the "Four Great Academies" refers to the Four Great Academies of the Northern Song.