390s BC

Mathematics

Platonist Theaetetus [b. Athens, Greece, c. 415 bce, d. Athens, 369 bce] extends the Pythagoreans' work on incommensurables -- what modern mathematicians recognize as irrational numbers. He treats not only square roots but also other types of geometric incommensurables and classifies them. His work (and that of Eudoxus) is thought to be the basis of Book X of Euclid's Elements. See also 410 bce Mathematics; 380 bce Mathematics.

Greek mathematician Archytas [b. Tarentum (Italy), c. 420 bce, d. c. 350 bce] builds a series of toys, among them a mechanical pigeon propelled by a steam jet. He is also credited by some with the invention of the pulley. See also 700 bce Tools.

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Millennium:	1st millennium BC
Centuries:	5th century BC - 4th century BC - 3rd century BC
Decades:	420s BC 410s BC 400s BC - 390s BC - 380s BC 370s BC 360s BC
Years:	399 BC 398 BC 397 BC 396 BC 395 BC 394 BC 393 BC 392 BC 391 BC 390 BC
Categories:	Births - Deaths - Architecture Establishments - Disestablishments

Deaths

Socrates 399 BC

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