Pantheon, Rome Italy (c. 118 – 125 CE)
Rome’s Pantheon is the largest unsupported concrete dome in the world, a startling record since building technology has come so far. Its dome has presided over the city of Rome since the time of Hadrian, who built it to honor multiple Roman gods. The niches around the building once held statues of various gods. The oculus, a 9 meter(29 foot) round opening at the peak of the dome, is the main source of light and fresh air. There is no glass in the oculus; when it rains, the floor gets wet. Fortunately, there are drains in the floor to help with pooling water. During certain times of the day and year, the sun shines through the oculus like a spotlight, shining on (or just above) the statues, highlighting each one in turn. These are just the famous features. The Pantheon is full of unsolved secrets.