Medieval James Himself

Medieval James Himself
Guide at Ozark Medieval Fortress

Friday, January 7, 2011

13 Knots

“How did they measure on the job in the 13th century?”  Great question and close to the heart of Michel Guyot, who started Ozark Medieval Fortress.  Remember the Middle Ages predates use of the metric system. That was introduced after the French Revolution, which is after the American Revolution and a long time in the future.  They used the Standard System, which now people in the U.S. think means American.  It doesn’t. It means Human system. The inch was the width of the thumb or two fingers. The palm was four fingers. The heart of the system was the extended tip of thumb to extended tip of little finger.  In French that’s the “empan”, a term heard often at the Ozark Medieval Fortress.  In English, it is the “span” and in German it is “die Spanne”.  Women thought in terms of the span because their lives were so tied to making textiles. The benefit of the span is you can “walk” your hand in making measurements.  Many elderly ladies on tour have said they remember their grandmothers measuring with the span.  Incidentally, later in the 1800’s, with steam power and plentiful material, ladies measured material by the “yard”, from their nose to extended hand.  Men thought differently. No surprise there.  Usually on bigger projects they measured by the two-span, or “foot”.  U.S. men still do, except for some teenagers who play football and see things by the yard.

13 Knot RopePic 3A rope was made with a loop knot at the beginning and 12 more knots spaced with an empan between each knot.  That made 12 spaces.  On a job site, it is important that the workers understand instructions and the workers could typically only count as high as twelve.  There were no schools, but they learned twelve because of the Christian Church with the 12 apostles.  On a carpentry job, the empan of the Master Carpenter was the measure for the ropes. On a masonry project, such as the castle, it was the empan of the Master Mason.  At the Ozark Medieval Fortress, the empan is that of Michel Guyot.  At the rope maker hut they have a board with pegs set at his empan so all the 13-knot ropes they make for the laborers are the same.

The 13-knot rope is more than a tape measure.  It is a compass and protractor as well.  The builders knew the value of arches from the Romans and many were used in the Middle Ages.  The curve of an arc was easily made by using the end loop of the 13-knot rope as a center and selecting the appropriate knot for the radius.  As a protractor, two workers would use the 13-knot rope to create triangles.  An equilateral triangle appears with three sides of 4 empan each.  This makes an excellent steep angle for roofs that won’t leak whether covered with tile in France, slate in Germany or thatch in England. Modifying the triangle to 10 empan with 4 on the base and 3 on each side gives the famous Egyptian pyramid triangle.  This was used a lot for roofs, bridge bracing, and even the plumb bob level of tapril29 (85)bhe Middle Ages.  A right angle, which is so valuable as a poor man’s square, can be made with three, four and five empan.  With the right angle triangle, they created square doors, tables, shutters and windows and shipbuilders could have true perpendicular thwarts and masts. 

The laborers of the Middle Ages were primitive, but skilled, industrious and clever. We often underestimate them. 


  1. Interesting knowledge. Dad would be very proud.

  2. Takes those old geometry lessons to a whole new perspective!