The pantheon was built almost entirely of concrete, save the porch which was also constructed of marble. From the outside of the domed section, it would appear to an onlooker to be made out of brick, but this is not the case. The bricks in this section are only a veneer, or thin decorative layer. Simple lime mortar that was popular during the period was made by combining sand, quicklime, and water. When the water evaporated, the concrete was set. Roman concrete used in the construction of the Pantheon, called pozzolana, acted quite like modern Portland cement and would set even when the mixture was still wet. Hadrian designed the Pantheon’s domed top to be 43.3 meters in diameter, which is also the exact height of the interior room. A cross section of the rotunda would reveal that it was based off of the dimensions of a perfect circle, and that is what makes the interior space seem so majestic. The sheer size of the dome was never replicated or surpassed until the adoption of steel and other modern reinforcements. What made Hadrian’s dome possible though was his use of concentric rings laid down one after the other over a wooden framework to create the basic shape of the dome during construction. The rings would apply pressure to one another, thus stabilizing the structure. The lower portion of the dome was thick and made of heavy concrete and bricks, while the upper portion was built thin and utilized pumice to make it lightweight.

The exact purpose of the front porch is unknown, and as mentioned before, may have only been added in order to give the building a façade. “It consists of a pedimented roof, supported by no less than sixteen monolithic columns, eight of grey Egyptian granite across the front, three on either flank, and two behind them on each side.” By adding this colonnade Hadrian had proven that he saw past what man had originally used it’s temples for. Traditionally, the temple cella would never be entered by the public, and so architects would hone and focus their craft on the exterior elements of the temple. Hadrian had effectively