The Arch of Trajan is a granite Roman gateway, around 14 metres high, standing astride a narrow street near the Plaza de España. It was probably the monumental entrance to the provincial forum precinct rather than a true triumphal arch — and its association with the emperor Trajan is traditional rather than documented. Originally it would have been faced in marble; the bare granite core is all that remains.
Look up as you walk under it: the keystone and springers are still in place, the curve is geometrically perfect, two thousand years of weather have not put it out of true. There is nothing to pay and nothing to queue for. It is one of those Roman survivors that has simply continued doing its job — letting people through.