One of the great adherents to the observation and veneration of the Sun was the Roman Emperor Hadrian.  When he restored the Pantheon in the second century AD, it conveyed a clear message to Roman citizens, echoing the assertion of Akhenaten almost fifteen hundred years before him: the Sun is the physical manifestation of our God.  A half-century earlier, Nero had set the pattern when he built an octagonal room with a dome, which was inspiration for the Pantheon.  He designed this dome with an ‘eye’ or oculus that used Sunlight to mark his important anniversaries on the walls.  Originally built by Marcus Agrippa, whose name is still shown on the triangular porch façade – the only remaining part of his effort - the Pantheon was destroyed in the fire of AD 80, restored, burned again thirty years later, and then was completely rebuilt between AD 118 and AD 128 by Hadrian.  It was he who completed the forty three metre wide dome, with its open hole or ‘oculus’ at top, which today remains the largest unsupported and unreinforced concrete dome in the world.
 
Visitors to the building could essentially tell time by observing the position of the shaft of light from the oculus, which crosses above or below the entry at noon.  Furthermore, the beam hovers directly above the door at the March and September equinoxes, both moments of ceremonial importance for ancient Romans because it was then that emperors -many of whom cultivated an association with the Sun deity - were considered closest to the heavens and gods.  The midday Sun on April 21 – the date commemorating the founding of Rome, as declared by Hadrian - spotlights anyone who stands in the open doorway of the Pantheon.  The emperor would have entered the Pantheon at that very moment each year, the bright halo around him acting as a striking confirmation of his divine power and the glory of Rome.  Emperors before Hadrian had focused their attention on the Sun, but it was Hadrian who demonstrated that he drew his authority from the solar source and could command in its name.  As with the Egyptian pharaohs, his subjects believed he controlled its influence here on Earth.
 
Credit for Images at top of page:
(L) http://www.romanhomes.com/your_roman_vacation/quarters/images/pantheon-aerial-view-h14-m5-t.jpg
(R): http://www.digital-images.net/Gallery/Scenic/Rome/Scenery/Pantheon/pantheon.html