Puzzle of

Two millennia

The Alcántara Bridge was built in 104-106 CE by Trajan’s legions. It lasted for more than a thousand years without significant maintenance (except for the triumphal arch); it’s only been repaired a few times in its second millennium.

The dam behind it was built in 1969. How long will it last without maintenance? I’m betting the dam is the greatest threat to the existence of the bridge that the latter has ever faced.

Does the bridge represent grotesque overbuilding on the part of the Romans? What’s the point of a bridge you don’t have to repair for longer than the expected lifetime of your civilization? Or rather, not “what’s the point?” but “is this the best use of resources?” I have no data, but I’m prepared to bet that more man-years of work went into the bridge than into the dam.

Speaking of which — the dam is on the Tagus River, just before it leaves Spain to go into Portugal. Since it was constructed there have been more droughts on the Portuguese side than on the Spanish side. Wars have been fought for less.

Credit: jotahoyas

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