The distinctive shape of the "onion dome," a curved roof structure that draws to a point at the top, can be seen widely atop religious structures in Eastern European nations such as Russia and Poland.

Some of the most recognizable are attached to Moscow's St. Basil's Cathedral.

The dome's uniquely expressive shape has a very practical origin; sent abroad by Russian czars such as Ivan the Terrible, architects traveled to sometimes very distant cities, including Constantinople, home of the Haghia Sofia.

Impressed by that structure's magnificent dome, the architects brought the concept back in the hopes of recreating it in Moscow--they failed.

The traditionally built round domes couldn't support the weight of the heavy Russian snow, and kept collapsing. So the architects' answer was to create a structure off of which the snow would simply slide--hence, the onion dome.

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