Arabic mile

The Arab, Arabic, or Arabian mile (الميل, al-mīl) was a historical Arabic unit of length. Its precise length is disputed, lying between 1,800 m and 2,000 m. It was used by medieval Arab geographers and astronomers. The predecessor of the modern nautical mile, it extended the Roman mile to fit an astronomical approximation of 1 minute of an arc of latitude measured along a north–south meridian. The distance between two pillars whose latitudes differed by 1 degree in a north–south direction was measured using sighting pegs along a flat desert plane.

There were 4,000 cubits in an Arabic mile. If al-Farghani used the legal cubit as his unit of measurement, then an Arabic mile was 1,995 meters long. If he used al-Ma'mun's surveying cubit, it was 1,925 meters long or 1.04 nmi

During the Umayyad period (661–750), the "Umayyad mile" was roughly equivalent to 2285 m, or a little more than 2 km, or about 2 biblical miles, for every Umayyad mile.

Al-Ma'mun's arc measurement
Around 830 AD, Caliph Al-Ma'mun commissioned a group of Muslim astronomers and Muslim geographers to perform an arc measurement from Tadmur (Palmyra) to Raqqa, in modern Syria. They found the cities to be separated by one degree of latitude and the corresponding meridian arc distance to be 66⅔ Arabic miles and thus calculated the Earth's circumference to be 24,000 mi. Using this measurement, knowing that earth's circumference is 40,007.683 km makes the Arabic mile little more than 1,666.994 metres. With Firuzabadi in his famous dictionary saying that a mile equals 3000 old dhira (ie cubit) this makes the dhira about 0.5556647 metres which is consistent with the tradition that kaaba height's is 27 dhira and its current height of 15 metres.

Another estimate given by his astronomers was 56⅔ Arabic miles (111.8 km per degree), which corresponds to a circumference of 40,248 km, very close to the current values of 111.3 km per degree and 40,068 km circumference, respectively.