Construction

A Rope with 13 Knots

At Ozark Medieval Fortress, you won’t see any modern equipment. No digger-dumper, cranes, or yellow-helmeted surveyors and engineers are to be found on site.

Instead, a 13-knot rope is used by the workers to work out the mathematics and geometry demanded by such an ambitious building.

A rope with 13 knots was used in Medieval times as a measuring tool. It was an early version of the ruler that we use so often today. The use of a rope with knots as a measuring tool dates back to Egyptian times.

Over the years the number of knots in a measuring rope varied. The master builders of Medieval times, the builders of castles and cathedrals, used 13 knots in their measuring ropes.

Why 13 knots?

A rope with 13 knots is a rope with 12 equal spaces. With 12 equal spaces, master builders could form many geometric shapes, including three kinds of triangles – equilateral, isosceles, and scalene.

A rope with 12 equal spaces was a tool from which an apprentice could easily learn addition, subtraction, multiplication, and division. 12 is a number that can be divided evenly by 2, 3, 4, and 6.

A rope with 12 equal spaces was an essential tool for designing an arch.

A rope with 12 equal spaces was a tool that artisans used to share important measurement information.

The number 12 was a number that was very familiar to people who lived in Medieval times. There were 12 months in the year. Each day was 24 hours long, that is, two times twelve. There were 12 apostles, and 12 signs of the zodiac.

The rope with 12 equal spaces led directly to the invention of the ruler that we use today for measuring, to the invention of a tool for drawing perfect squares, and to the invention of the compass.

At the Ozark Medieval Fortress you will see 13-knot ropes, and Medieval versions of rulers, tools for drawing perfect squares, pendulum levels, and plumb lines.

The Rope Maker

Project

Make a 13-knot rope.

Materials needed are: a rope, preferably made of hemp or jute, and
hands or a ruler, for measuring.

Simply start at one end of the rope and tie a knot. Then tie 12 other knots at equal distances from each other. Check that the distances are equal by folding the rope in half.

See how many geometric shapes you can make by folding the rope. Can you make a perfect circle using the 13-knot rope?

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