The Scandinavian mile is 10 kilometres long. It used to be longer still.
Many a traveller in Norway or Sweden has been misled by the Scandinavian mile – the “mil.” The milestone pictured above appears to indicate a distance of 5 miles. In modern international miles this would be a bit over 8 kilometres – a reasonable medium-sized walk. Reading it this way would be a horrible mistake, though. The milestone uses Scandinavian miles, not international miles. By that measurement the reasonable 8km walk transforms into an arduous 50 kilometre trek.
Prior to the mid-17th century CE every different region in (for example) Sweden had their own mil. These ranged from 6km up to 14.5km, which must have caused no end of confusion. In 1649 the mil was standardised to 36,000 feet… but this didn’t help. Like many now-obsolete feet, the Swedish and Norwegian feet weren’t standardised. At this time a Swedish mil was 36,000 Swedish feet, or 10,688 metres. A Norwegian mil was 36,000 Norwegian feet, or 11,295 metres.
Finally, in 1889, everything came into alignment. At the time Sweden and Norway were United Kingdoms, so they pulled together and redefined the mil as 10km exactly. Much simpler for the Scandinavians, still confusing to everyone else.
Today, fortunately, most Scandinavian signs and maps use kilometres instead of the mile, so the possibility for misunderstanding is much less. But it still sticks around in conversation and other informal contexts. Lurking silently, ready to jump out at an unsuspecting foreigner!
(End note: another interesting Scandinavian distance measure is the “rast,” which was defined as the maximum distance someone could travel before they needed to stop and take a rest. This seems like an exceptionally useful measure for people travelling on foot.)