
The domed ceiling of Bhaja Cave 12 has cross-arched wooden rafters that are inserted firmly into the rock, a construction method commonly utilized in cave architecture to reinforce the ceiling. Due to climatic conditions, the original timber structures have long since degraded. Even without these supports, the domed ceiling of the cave has remained intact for more than 2,000 years with only minimal damage.
For more details, go to the Encyclopedia of Buddhist Arts: Caves A-E, page 149.