Complex sentence: This line was once so frequently played that it has a separate code (D69) in ECO, though the lack of active counterplay for Black has made the main line of the Orthodox a backwater in modern practice.
Split into simpler sentences: This line was once so frequently played that it has a separate code (D69) in ECO. The lack of active counterplay for Black has made the main line of the Orthodox a backwater in modern practice.