April 2016 - In the time of the Roman Emperor Augustus, about 10 BC, one of his generals, a man named Agrippa, built a temple in the middle of downtown Rome "to all the gods". A temple to all the gods was called a Pantheon, which means all gods (pan= all, theon=of the gods, in Greek).
Now this temple was probably very fine, but we don't really know, because in 80 AD, in the reign of Titus, it burned down in a fire. Domitian built a new temple there, and THAT one burned down too. Around 120 AD Hadrian built a THIRD temple there in a more modern style (modern for 120 AD anyway!). This is the temple we have today. But to honor Agrippa, Hadrian left a message over the door saying that Agrippa had built the temple, as you can see in the picture.
You might think, well, that doesn't really look like much of a place. And from the outside it really doesn't seem very impressive. The Pantheon is built like a Greek temple on the front, with eight columns across the front like the Parthenon, and a pediment on top of that.
But on the INSIDE the Pantheon is one big giant dome, the largest dome ever built in the world up to that time - 43 meters in diameter (142 feet), and 43 meters from the floor to the top of the dome.
To hold up this dome, the builders had to make the brick and concrete six meters thick - about twenty feet! The coffering in the dome lightens it a little, but it's still very heavy. Nobody built a dome anything like this size anywhere in the world until Hagia Sophia in Constantinople in the 500s AD (but it's still smaller than the Pantheon). The first dome that was bigger than the Pantheon was in the Duomo of Florence in the 1400s, more than a thousand years later. Even then, the Duomo dome is about the same size, and nobody ever built another one of that size, until the 1800s with reinforced concrete.
Wait to the end to see the oculus
The hole in the top of the dome - the oculus- is open to the sky. Some people say the dome is so high that rain evaporates before it hits the floor, but that's not true - on rainy days, the marble floor just gets wet.
Learn by doing: try to build a round building with a dome in Lego or in Minecraft
Map of Rome showing where the Pantheon is
The Pantheon, by Lesley Dutemple (2002). Easy reading.
The Pantheon: Design, Meaning and Progeny, by William Macdonald (2002). Macdonald is a leading expert on Roman architecture. This one's not specially for kids, but good readers could get a lot out of it anyway.