So, i am in Rome and i saw the temple of antoninus and faustina. I read about the story of the high door and how the ground level used to be higher. Still, there is a doubt on my mind. If the ground was so above how come the base of the columns of the temple are on the lower (and more recent) level? Any roman or historian that canal answer me?
The temple has a complicated architectural history because it was converted into a church in the seventh or eighth century. Only the exterior walls and the facade (with the columns) are ancient, the main body of the building is the church, which was remodelled and rebuilt at various times. The door you can see from the forum is part of the baroque facade, built in 1602. The ground level had been above the ancient level for centuries, so the whole church building is many meters above the original temple level. Archaeological excavations have somewhat complicated the picture and made it hard to imagine, but there are some earlier drawings that can help (see here, here and here). On these you can clearly see the ancient columns disappearing below the ground, with the more recent doors at floor level. All of this was dug out when the forum was excavated, as the archaeologists went down the the ancient levels, and its these levels that modern tourists walk on.
Hope this helps!