Arch of Medinaceli -Medinaceli-, at Soria.
It is the only instance of a monumental arch composed by three gates in Hispania: a curious thing if we consider that these archs were often built in the Roman world. It shows a good state of preservation though hard weather of its geographic settlement did spoil its decoration. It was built at the top of a hill over Jalon river valley being almost 1.200 m. high in a very cold, rainy, windy, snowy area. Effect tried on this place was surprising people and showing greatness and power of Rome. Time has wasted ashlars, patterns and cornices, just leaving signs of past. Northern and Eastern sides, close to the village and mountain are better preserved, but southern and eastern sides looking to the valley are really spoilt. Anyway lower part, specially basement, is worse preserved: many ashlars have been restored.
Planta del Arco de Medinaceli
Plan of Medinaceli Arch.

Since it has almost totally lost its inscription surrounding the monument, written with golden letters, datation of the building has been difficult. At a first sight scholars thought that Trajanus Emperor constructed it, but later investigations concluded that it was built at Domitian age, at the end of 1st century. The arch was a part of the wall that gave the village shelter surrounding the top of the mountain.
It is built with Opus Quadratum of a different size, placed at a linear or -rarely- perpendicular way. Over them decorative elements were carved. Dimensions of the whole are 13,20 m. long, 2,10 m. wide and 9 m. high.
First level consists of four big pillars joined through vaults, forming two similar archs of 1,30 m. These are composed by seven equal voussoirs. They have a little archivolt that surrounds the exterior side. These two wholes -the lateral archs- are crowned by a moulding: central arch departs from it and made them elements supporting it.
Four elevations with an hypothetical original solution (Press images to enlarge).

A second level, crowned by a moulding similar to that of lower elements, consists of a central arch with 4,90 m. formed by 23 voussoirs and two lateral decorative wholes. They were formed by groove pillars with a corinthian capital, a pediment and two bases supported by its lower moulding, a little archivolt that surrounds its exterior side. At its four corners, there are four pillars with two façades bigger than the prior, following the same design. Over the capitals there is nothing today: a free ashlar comes to the moulding where this level ends. This room was covered by a possible inscription or a decorative element. It is a curious design: pillars at a second level but not at the first one. It is done because the wall close to this arch was as high as the first level. So excessive highness was at the level of both pillars.
Arco romano de MedinaceliArco romano  de Medinaceli
Both main façades of Roman Arch at Medinaceli. (Press images to enlarge).

Third and last level is composed by two files of ashlars crowned by a cornice. On these ashlars were fixed the golden letters that made the commemorative inscription. Some marks for supporting can still be seen. Its superior part, on the plan, let us see that ashlars forming the width of the whole were joined by supporting staples. They have a slight slope at both sides.
In short, this is a three gates arch, not very common. It would probably evolution to one gate archs. It had a commemorative function, but was also a door to the city. Central arch was made for carts and animals; lateral for walkers.