A Roman Emperor built this, for no particular reason at all.
It is the Heathen's Gate of Carnuntum but it isn't a proper gate, rather a monument: there's a column in its middle (partly reconstructed now) which very effectively would have prevented horsewaggons driving through this gate.
Also there was no reason whatsoever for anybody wanting to drive through the gate - as nothing of importance was located either side of it. The legions and civilians lived a couple of stadiums north of this place, the gate only was guarding millet and turnip fields.
But that's your classical Roman Emperor for you; they only ever thought about representation. (If you think about it, that's just the same with our politicians, isn't it?)
