In the seventeenth century a large number of books on fortification were published. [br]Every self-respecting author had his own system for calculating the dimensions of a fortress. Where one author worked with rectangular triangles only, another showed that he mastered the sine rule or even the tangent rule. Also, each author chose their own starting points with slightly different angles and lengths which made each fortress look slightly different. [br][br]Simon Stevin was one of the first authors in the Netherlands in 1594. He described the ideal forms of a regular fortress.[br][br]More informatie is available at my website [url=http://www.fransvanschooten.nl/Stevin.htm]fransvanschooten/Stevin[/url].[br]This page belongs to my GeoGebra book [url=https://www.geogebra.org/m/xeqjdkpj]Fortification in the Netherlands in the 16th and 17th c[/url]entury.[br]