Peter Kingdon Booker
Following a question at my last lecture on the exact value of the league, I have put in a little research and find the following.
The Romans picked up this word in Gaul and defined it as 1.5 Roman miles (7,500 Roman feet, 2.2 km, 1.4 mi.)
It is still used in some parts of Latin America in its original meaning which was the distance that a person – or a horse – could walk in an hour. This concept is capable of giving many values since physical fitness and quality of road can lead to greatly different values around the 5.5km mark.
The English speaking world valued the league at about 3 miles (I shall talk about the mile later) or between 4.8 to 5.6 km. Argentina has a league of 5.572 km; the Portuguese Empire had leagues of 6.1724km, 5.5556km, and 4.4444km, and later of 5km; Brazil still has the concept of a league valued at 6.6km; in France the league (lieue) has had several variants between 3.25 and 4.68 km; Spain originally used a league of about 4.2 km and this unit of measurement was abolished in 1568.
Summarising the above, in its history the league has represented values between 2.2km and 6.6km. The most likely value of the league used in the Treaty of Tordesillas was about 4.2km
The mile started its life with the Romans and represented a thousand paces (mille passuum) which is about 1,479 km
Queen Elizabeth I legislated in 1592 the value of the Statute mile (hence the name of statute mile) at 5280 feet (1.6km) but it was only in 1959 that the English speaking world agreed the value of the international mile at 1.609344km. Before the Statute of 1592, the Irish mile had been 6720 ft (2.04km) and the Scottish mile was 5951 ft (1.803km).
The nautical mile is defined internationally at 1.852km (the length on the ground of one minute of arc along a meridian of the Earth). The US Survey mile is1.609347km
Danish miles were 7.5325km; German miles were between 7.4127km and 7.586km;; in Russia it was 7.468km; in Croatia 11.13km or 7.586km; the data mile is 1.8288km; the metric mile (a sports term) represents a distance of 1.5km except where in the US it represents 1.6km
The Swedish mil represented a distance between 6km and 14.485km, depending on which province was using it and it was standardized on 10.687km in 1649; in Norway it was 11.298km. In Norway and Sweden the term mil is still in use and represents 10km.