Zanzibar historic site, Stone Town, where slaves were sold, is falling victim to neglect. "We are in a race against time," said Mwalim A. Mwalim, director of the government conservation authority. "Now it's almost too late." Of Stone Town's nearly 2,000 buildings, "the majority are in poor to ruinous condition."

Five years ago, Stone Town received a boost when the United Nations awarded it World Heritage status, recognizing it as a historically intact East African coastal trading town that is also a living community. And the town is luring more tourists, who browse the shops and spice stalls along the winding streets.

Yet the core problem remains: Stone Town is no longer a well-to-do trading center. Most of its 16,000 residents are poor and pay highly subsidized rents to Zanzibar's government, which owns half the town but lacks money for preservation projects.