This is the last bridge I visited in Stockholm, and I think it's also the oldest. Designed by Erik Palmstedt and Carl Fredrik Adelcrantz, it was completed in 1797, replacing a previous timber bridge which had been extensively damaged by flooding in 1780. The part of the bridge that I saw comprises three 16m span stone arches, although the structure continues south on a series of vaults on the island, and a further arch span over another waterway.
Klas Lundkvist's report Norrbro och Strömparterren, available online, has a great deal of information on the bridge and its construction. Lundkvist suggests the design was inspired by French architecture, particularly Perronet's 1774 Pont de Neuilly.
A 1781 drawing shows that the masonry piers are supported on timber piles. A later drawing shows the piers constructed on the pilings by layering stone within an open-topped timber caisson, the base of which was left in place to form a timber layer above the piles. This method was reportedly also used for the Pont de Neuilly. Below the bridge, it can be seen that there are actually two parallel sets of arches, and holes are visible which would have formed the support positions for temporary timber centering during construction.
The bridge is in very good condition, with the ornamental balustrades in particular looking like they have been recently renewed.
I think the arches and piers are too squat for the bridge to be considered truly elegant, but it certainly gives the impression of robustness, and I'd expect that having lasted for 219 years so far, it could quite easily last the same again.