Measuring with a rope

I’ve already written a little about the tanab, the traditional rope-measuring device that Munajjim Yazdi and his team used to record the distances that Shah Abbas walked in 1601.  As chief astrologer, Yazdi was a measurement expert – also using his astrolabe (click here to see a slightly later Safavid astrolabe) to compute how fast the Shah travelled on at least some of his many journeys.

During my fieldwork, I wanted to see how easy it might be to use a 40 metre length of rope to measure distances, whilst a group is walking – and I was surprised to find that, with three (or maybe four) dedicated people, and an agreed system, it is surprisingly simple.

When I tried this out near the very beautiful Sardahan caravanserai, we assessed accuracy by comparing the rope measurements with those obtained using a GPS – surely the very first GPS-rope comparison – and found that the rope was really quite accurate.

To add to this, one section of the 1601 walk allows a more comprehensive evaluation of the various possible measurement systems. Along the Khurasan highroad to Mashhad, Yazdi gives specific names for two adjacent stopping places: the Ribat-i Ahuan, and the Ribat-i Qusha. Since these buildings are both extant, and visible on Google Earth, it is easy to measure the distance between them.

The satellite distance is, unsurprisingly, slightly less than that measured by Yazdi – it’s an exact crows-fly distance, while the walkers can’t have walked in a precisely straight line, and will also have to have climbed over any small elevations in the terrain.

The Khurasan road is, as Professor Melville has said, “well-worn”; and in the nineteenth century, many Europeans wrote books about their journeys in Khurasan, including records of the distances they travelled. European travellers generally halted at the caravanserais, but these are both near the ribats. In Ahuan, the two are effectively adjacent; while in Qusha the two are about 500m apart.

The table here shows how consistent most of the estimates are – at least in farsakhs.  The mile estimates, on the other hand, vary wildly – from 11.5 (Houtum-Schindler) to 32 (Baker – both in 1876). Perhaps the farsakh distances were as suggested by the local guides; but the Europeans themselves estimated the number of miles they travelled – including my favourite, Eastwick, who solemnly included his hunting time.