Euclid's Elements and other remnants from ancient Greek times contain theorems about triangles and descriptions of four triangle centers: centroid, incenter, circumcenter, and orthocenter.
Later triangle geometers include Euler, Pascal, Ceva, and Feuerbach. In 1873, Emile Lemoine presented a paper "on a remarkable point of the triangle," now known as the Lemoine point or symmedian point. This paper, writes Nathan Altshiller Court ( Court also describes seminal papers by Henri Brocard and J. Neuberg and names Lemoine, Brocard, and Neuberg as the three co-founders of modern triangle geometry. |

An astonishing wave of interest and publications in triangle geometry swept through the last years of the 19th century and then collapsed during the early years of the 20th.

However, many new gemstones in the fields of triangle geometry remained to be unearthed with new excavating tools, such as computers and methods from other areas of mathematics. All of this has led to the state of the art up to 1995, as described in

**Philip J. Davis**, "The Rise, Fall, and Possible Transfiguration of Triangle Geometry: A Mini-history," *American Mathematical Monthly* 102 (1995) 204-214.

Among authors of frequently cited books in triangle geometry are the following:

Nathan Altshiller Court (1881-1968), author of *Modern Geometry*

Roger Arthur Johnson (1890-1954), author of *Advanced Euclidean Geometry*

William Gallatly (1850-1914), author of *The Modern Geometry of the Triangle*

John Casey (1820-1891), author of 19th century books specializing in triangles and conics

Charlotte Angas Scott (1858-1931), author of *An Introductory Account of Certain Modern Ideas and Methods in Plane Analytical Geometry*

Among those for whom triangle centers (or central lines, etc.) have been named are

Napoleon Bonaparte (1769-1821), as in *Napoleon theorem*

Giovanni Ceva (c1647-1734) as in *Ceva's theorem, cevians, cevian triangle*

John Wentworth Clawson (1881-1964) as in *Clawson point*

Leonhard Euler (1707-1783), as in *Euler line*

Karl Wilhelm Feuerbach (1800-1834), as in *Feuerbach theorem*

Joseph Diaz Gergonne (1771-1859) as in *Gergonne point*

Ludwig Kiepert (1846-1934) as in *Kiepert hyperbola*

Emile Lemoine (1840-1912) as in *Lemoine point* (or *symmedian point*)

G. de Longchamps (1842-1906) as in *De Longchamps point*

Gian Francesco Malfatti (1731-1807) as in *Malfatti problem*

Frank Morley (1860-1937) as in *Morley triangle, Morley points*

Christian Heinrich von Nagel (1803-1882), as in *Nagel point*

Joseph Jean Baptiste Neuberg (1840-1926) as in *Neuberg circles*

Kurt Schiffler (1896-1986) as in *Schiffler point*

Robert Simson (1687-1768) as in *Simson line*

Sir Frederick Soddy (1877-1956) as in *Soddy circles*

Jakob Steiner (1796-1863) as in *Steiner ellipse, Steiner point*

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