A view as we left Hagia Sophia. It is an unforgettable architectural structure. I hope it stands forever. The research on it by the Smithsonian worries me.

In addition to the obvious challenges—leaks, cracks and neglect—an invisible menace may pose an even greater danger. Istanbul sits squarely atop a geologic fault line. "There most definitely are seismic threats to Hagia Sophia, and they are great," says Stephen J. Kelley, a Chicago-based architect and engineer who consults on Byzantine churches in Turkey, the former Soviet Union and the Balkans. "One tremor and the whole thing could come falling down."

A view as we left Hagia Sophia. It is an unforgettable architectural structure. I hope it stands forever. The research on it by the Smithsonian worries me.

In addition to the obvious challenges—leaks, cracks and neglect—an invisible menace may pose an even greater danger. Istanbul sits squarely atop a geologic fault line. "There most definitely are seismic threats to Hagia Sophia, and they are great," says Stephen J. Kelley, a Chicago-based architect and engineer who consults on Byzantine churches in Turkey, the former Soviet Union and the Balkans. "One tremor and the whole thing could come falling down."