The Bridge They Said Would Never Hold

In 2009, engineers in rural Rwanda faced an impossible problem. The Nyabarongo River had swallowed every bridge the government tried to build during rainy season. Contractors rejected the local volcanic stone as too porous, too irregular, too unreliable. They shipped in steel and concrete from Kigali instead. Each time, the floods won. Then a young Rwandan engineer named Celestin Habiyaremye suggested what everyone else had dismissed — using that same volcanic basalt, anchored deep into the riverbed the way his grandfather had described village builders doing generations ago.…