Parries Luke's aggressive attack

Vader parried, blocked, parried again, and found himself being forced backward by the aggressiveness
and skill of Luke's demonic attack. The breath mask tilted back for a second. A section of heavy basrelief on one of the supporting pillars was loosened, fell away.

At the last instant Luke sensed it, jumped backward. The huge carved panel shattered between them.
Both men rested uneasily as the dust settled. Luke gulped for air, while Vader showed less aplomb and
increasing tension.

Splinter of the Mind's Eye, Chapter XII, 122