The Pantheon is an ancient Roman temple in central Rome that has served as a Catholic church since 609, officially known today as the Basilica of St. Mary and the Martyrs (Santa Maria ad Martyres). It looks amazing in watercolour
 
Originally a temple “of all the gods,” the Pantheon is now one of the best‑preserved buildings from classical antiquity, in large part because of its early conversion into a church. It stands on the Campus Martius and opens onto the Piazza della Rotonda, remaining a major religious site and tourist landmark.
 
The building combines a traditional temple front—portico with massive granite Corinthian columns and pediment—with a vast circular rotunda behind.
Its unreinforced concrete dome, about 43.3 meters in diameter and equal in height, is still the largest of its kind in the world.
At the crown of the dome is the oculus, an 8.7‑meter‑wide circular opening that provides the only direct light source and a symbolic link between interior and sky.
 
Despite being built by Hardian the inscription on the façade still credits Agrippa. As Agrippa built the first Pantheon in 120CE.
 
Interesting facts....
Its unreinforced concrete dome, about 43.3 meters in diameter and equal in height, is still the largest of its kind in the world.