'...a Word or two of Dimensurators or Measuring Instruments, whereof the mosts usual has been the Chain,
and the common length for English Measures 4 Poles, as answering indifferently to the Englishs Mile and
Acre, 10 such Chains in length making a Furlong, and 10 single square Chains an Acre, so that a square
Mile contains 640 square Acres...'
John Ogilby, Britannia, 1675

Fig.1 - illustrations from John Ogilby's Britannia of 1675.
left - cherub holding chain. centre - complete chain folded at front of table.

Fig.2 - detector found 20 and 30 link tags
Featured in Figure 2 are two brass artefacts that have puzzled many archaeologists and metal detector users for some time. They have previously been published in archaeological excavation reports2 and detector magazines where their use has been suggested to range from harness pendants to amulets and their date range from Roman to Medieval but in fact they do not predate c1620AD.

The use of a chain for surveying and measuring was first recorded in 1579. Edmund Gunter (1581-1626) Professor of Astronomy at Gresham College, London was a mathematician who by the 1620's had designed a chain consisting of 100 iron links measuring 66 feet (22 yards). Its usefulness was such that it became the principle means for the linear measurement of land for almost 300 years. The invention of the steel tape in 1867 brought a more convenient and accurate means of measuring large distances and therefore by the early 1900's Gunter's Chain had generally fallen out of use.

The chain was marked at every 10 links along its length by brass tags or tallies, the number of points on the tag denoting its position on the chain. At 10 links the tag would have a single point (fig.5); at 20 links 2 points (fig.2 left); at 30 links 3 points (fig.2 right) and at 40 links 4 points (fig.5). This was then repeated inwards from the other end of the chain, with the centre usually having a round disc as a marker. See fig. 3 for a full chain and the relative positions of the tallies. It is of course these tags that we occasionally find with detectors out in the fields. At each end of the chain was a carrying handle usually made of brass and these too may be found - an example can be seen in fig. 4. Some later chains may have makers' marks on the handles or tags but generally they are very difficult to date with any accuracy.
Gunter's Chain - also called a 'Survey' or 'Agricultural' chain - was based on a very ancient measure of the breadth of a furrow or plough strip. Gunter's measure can be summarised as:-

1 link = 7.92 inches
25 links = 1 rod (pole or perch) or 16 ft
100 links = 1 chain or 66 feet/22 yards
10 chains = 1 furlong ('furrowlong') or 220yds
80 chains = 1 mile or 5,280ft/1,760yds
10 square chains = 1 acre

The chain has a decimal basis i.e. 1/100th chain is 1 link. Measurements are made in chains and decimal parts which are expressed in links (for example) 4.25 chains equals 4 chains 25 links. Using this system it was reasonably easy to work out acreage by multiplying together length x width of the chains (plus any odd links) and then dividing by ten to give the total acres. These chains were commonly used by landowners and farmers as well as surveyors hence the occasional loss of the marker tallies or tags. In America vast areas had to be surveyed and several variations on the basic chain developed including the '2 Pole' and the 100ft 'Engineers' Chain.3 It will be noted also that the chain is the exact measure between the stumps of a cricket pitch - I wonder if there are still any of these old chains languishing to this day in some dusty corner of a Victorian cricket pavilion?

Fig.3 Gunter's Chain

Fig.4 Gunter's Chain handles Fig.5 Gunter's Chain tags

1. Thanks to Martin and Jean Norgate for allowing use of their website's Ogilby text and pictures
2. St. Peters Street, Northampton. Page 259, Fig.112:109
Gadebridge Park Roman Villa. Page 133, Fig.58:84
3. surveyor's chain