How were the Inca fortresses built? Inca technology was simple. They had no written language, knew few basic machines, did not use the wheel or the block and tackle, and smelted no high-strength metals. They maximized their Late-Stone-Age technology with a genius for communication and organization.

The Inca fortresses have survived many centuries of violent volcanic earthquakes; indeed, they have survived better than solid European-style colonial buildings. They are constructed of massive stones fitted to one another with complex, knife-edge precision joints that bind the structure even when the ground trembles. A razor blade still cannot be inserted between them. How did the Incan craftsmen shape and fit together such enormous stones without metal tools?

Architect Vince Lee helped us figure out one way in which the Inca could have handled the smaller stones. But how the Inca carved and fitted together 100-ton blocks of stone remains a mystery. On May 12, Lee responded to questions during a live event, and to additional questions e-mailed to this Web site for one week thereafter. Check out the archived questions and answers.