The Great Mosque of Samarra, Iraq

When the Great Mosque of Samarra (in Iraq) was built by the Abbasid caliph Al-Mutawakkil (reigned 847–861) around 850, it was probably the largest mosque in the world, with a total area of nearly 42 acres. The mosque was built out of baked brick, with an interior decorated with blue glass. Most of the structure was destroyed during the Mongol invasion led by Hulagu in 1258, but one of the most-intriguing features, the 170-foot (52-meter) minaret, survived. The minaret is built in the shape of a cone, wrapped in a spiraling ramp that leads to the top. It’s unclear why the builders chose the conical shape; some people have noted that it slightly resembles an ancient ziggurat.