I haven't done any research on this, so I'll just post the title from the Reddit entry.
The oldest door still in use in Rome, Pantheon. Cast in bronze for emperor Hadrian's rebuilding, they date from about 115 AD. Each door is solid bronze seven and a half feet wide & twenty-five feet high, yet so well balanced they can be pushed or pulled open easily by one person.
Some readers here may have more information, or may have seen the door. The discussion in the thread at the via is trivial, but I did find a link to an interesting subreddit entitled Human For Scale.
Question for my copyeditor/poofreaders and other bored English majors: Is this a door (with two swinging parts), or are these two doors that meet in the middle?
Addendum: A tip of the blogging cap to reader Bob, who sent me a link to a webpage at Finding Ancient Rome, which has more information on this door/these doors:
And below this humble ceiling is the only door in the rotunda, the great double bronze door which was long thought to be a later replacement for the original, mainly because of the frame on either side and the grille above, which caused archaeologists to comment that it was too small for the opening. In fact, when at last the bronze was carefully studied, these were found to be original Roman doors, one of the rare survivals of monumental bronze. They had been cleaned in the course of the centuries, Christian motifs applied, but analysis of the fusion technique left no doubt that they date from the empire.
Each half of the double door weighs 8.5 tonnes, and rotates on pins set into the floor and the architrave above. An ingenious but laborious and little understood system allowed removal of the wooden architrave and replacement of the pins which tend to wear. In 1757, during an attempt to keep the door working, the whole thing fell, killing the foreman trying to remount it.
The right door was left totally blocked and the left door would open only partially. Two centuries later, after much careful study, using just soap (!) and specially-made plates to slightly lift the doors, the pins were replaced, the doors put back into their seats, and finally both could be opened and shut. It was 1998; the doors had not been fully opened for 241 years.