While writing my essay on how to drain a swamp, I found the need to explain the continued use of rods as a unit of measurement, a modern holdover of several ancient measurement systems. Because engineering can be a very conservative field, US drains, to this day drain widths are often specified in rods, or in units width that equal 16.5 feet (16.5 feet= 1 rod). Why 16.5 feet? In part because a rod is 1/4 the length of the standard 100 link surveyor’s chain, 1/4 of 66 feet = 16.5 feet = 25 links of the chain. A chain, 66′ is 1/80 of a mile, and a mile is 1000 double paces of an Elizabethan legionnaire (left-right = 1 pace); Mille = 1000 in Latin. A Roman mile is shorter, but ancient Romans were shorter people, with shorter strides. A furlong was originally the distance an ox-team could plow in a day, but was redefined to 1/8 mile, or 10 surveyor’s chains.

Gunter’s chain (surveyor’s chain) = 1/80 mile or 44 Roman cubits. The rod is 1/4 this, or 25 links. The acre is 10 square chains. A city block is 1/20 mile or 4 chains.

Getting back to the 66 foot, surveyors chain, this is called Gunter’s chain. It was first made in 1620 and adopted in England in the mid 1600s. The length is convenient, not only because 10 chains equal a furlong and 80 equals a mile, but because an acre is 10 square chains, and a square furlong = 10 acres. By US law of 1790, all US surveys were to be done in units of these 66 foot, Gunter’s chains, and this will law will explain why land plots are the size they are throughout the US and (probably) in England to this day. Roads are this size, I speculate, because the land plots are this size, and because engineering is conservative.

To show how conservative engineering is, a rod equals 11 standard (English) cubits where each standard cubit = 1.5 English feet. A Roman cubit = 1.5 Roman feet =  17.5 inches (Roman feet were smaller); Greek cubits and standard Egyptian cubits were about this length too, 17.5″ ±1/4″, and this is also the Hezekiah’s Biblical cubit (or amoh in Biblical language). We know the Biblical cubit because the length of Hezekiah’s channel was stated to be 1,200 cubits, and the measured length is 1,749 feet. Dividing the one by the other, we find the measure of Hezekiah’s cubit was 1.46 feet, or 17.5 inches. There was a larger cubit used in Babylon and Egypt for royal construction. It was the basic cubit measure plus the width of 4 fingers for a total length of 20.7″. A Royal Egyptian cubit is shown below. This also appears to be length of the Jewish, Talmudic cubit, though some expand it to 21.5″ because we, today are bigger.

Royal Egyptian cubit (meh niswt) 20.7″ and other, Egyptian weights and measures, Louvre museum.

To show how conservative engineering is, the average length of a New York block is 1/20 mile or 4 chains. The average east west street is one chain, 66 feet (most NY streets are 60 feet, with 15 wider ones, like 42nd st., 100 feet). A typical US rural road width is 1/2 chain, 33 feet, where the two traffic lanes are 11 feet (US law allows 10-12 feet) and the remaining 11 feet is divided to provide a shoulder on each side (4 feet is the target minimum shoulder). When there are ditch-drains on the side of the road, an effort is made to put these beyond the shoulder. The drain commissioner, a post I was running for, had responsibility for these ditches. The main drain of Oakland county is 66 feet wide, one chain, for its underground length, and 25 feet (1.5 rod) tall. It then passes under Dequindre road (a 66 foot wide road), and expands to an open ditch, 66 foot wide at the bottom but 132 feet wide at the normal top. It might be argued that these dimensions are coincidental, but I suspect they’re holdovers from older, successful construction projects elsewhere.

One last thing, sports. I suspect the reason that Canadian football fields are 110 yards long, and that Lacrosse fields are the same is that 110 yards is 5 chain. Similarly, I suspect that Cricket pitches are 66 feet is because 66 feet = 1 chain. As you can see, the past isn’t quite dead, and isn’t quite past either.

Robert E. Buxbaum Nov. 29- December 3, 2016. I hope you like this discursion into ancient measures. If nothing else it helps me remember the size of an acre = 1 chain x 1 furlong, and the size of the cricket pitch, in case I should ever be called upon for that information.