The temple was rebuilt by Emperor Hadrian in about 126 CE. It is a circular building, with eight massive granite columns in front and two groups of four behind. With its high brick walls and impressive columns, the Pantheon makes an immediate impression on its visitors. The only source of light was the central opening, the 'oculus'. This was a characteristic of Classical architecture since the 16th century.

It is one of the best preserved of all Roman buildings. Since it was built, the Pantheon has been continually used. Now it is a Roman Catholic church dedicated to "St. Mary and the Martyrs", informally known as "Santa Maria Rotonda.