What’s So Special About Rome’s Pantheon?

You really can't improve on perfection. Nearly two millennia ago, the Romans built the Pantheon in their capital, using concrete and little else to support the walls or the gigantic dome that sits on top. The temple was commissioned in 27 BC, during the reign of Augustus, but was completely rebuilt by the Emperor Hadrian around 150 years later. It has served as a Catholic church since the 7th century.

For over 1,300 years, the Pantheon boasted the world's largest dome, until its diameter (142 feet or 43.3 m, which is also its height) was surpassed by Florence Cathedral in 1436. The Pantheon remains the largest unreinforced concrete dome, and has had a huge influence on western architecture, on buildings such as Thomas Jefferson's Rotunda at the University of Virginia.

Engineers remain stunned by the Pantheon's longevity, since modern cement-based concrete offers no such durability. It wasn't until recently that researchers took a drill to a sample of the concrete that they began to understand what has kept the Pantheon relatively unharmed by nature or time: limestone and volcanic ash. The mixture creates strätlingite, a mineral that acts like modern microfiber and helps prevent the concrete from cracking.

Roman engineering: