This Gate which was the south entrance to the mercantile Agora was built by 2 slaves freed by Emperor Augustus in 3 BC.
The inscriptions on top of the Gate, which you can see from in front of Celsus Library indicate Mazaeus and Mithridates the Two freed slaves wished honor the Imperial family by building the structure.
This Gate provides some nice shady spot for tourist groups visiting Ephesus City in the heat of summer.
So Most of the Private Ephesus Tour Guides give a chance for a picture break for Celsus Library and set the meeting place to this Wonderful Roman Gate. In that sense the Gate is a life saver for many visitors.
What amazes me most is that there is almost 150 years time difference between the Gate of Mithridates and the Library of Celsus. The two structures are attached to each other they give such an amazing complete image together with no signs of age difference.