Twin Pillars

There are almost always two pillars.  In Ancient Egypt, two Obelisks sit outside many temples.  In Medieval Cathedrals, two pillars were placed to help determine the path and position of the sun, so they could be oriented correctly. In Alchemy and Hermeticism, the sacred knowledge is said to have been deposited inside two pillars. The Bible describes the two pillars said to have been positioned outside of the Temple of King Solomon.

There are variations, but there always seem to be two, twin, pillars.  Some of the symbolism is clear; they reflect the Spiritual principles of the unity of opposing forces.  That these physical monuments have other practical functions makes them all the more interesting. I am interested in examples of physical structures such as Obelisks and Pillars that typically appear as twins.  Do you have any examples?