Necessity (novel)

Necessity

Hardcover edition
Author	Jo Walton
Series	Thessaly
Genre	fantasy / science fiction
Publisher	Tor Books
Publication date	2016
Pages	331 (hardcover)
ISBN
Preceded by	The Philosopher Kings

Necessity is a fantasy/science fiction novel by the Welsh-Canadian author Jo Walton, published by Tor Books in 2016. It is the conclusion of the Thessaly trilogy, and the sequel to The Just City and The Philosopher Kings, which were both published in 2015.

In The Just City a city was created by the time-traveling goddess Athena on the island of Thera prior to its Iron Age volcanic destruction. It was then populated by philosophers and children from all ages of human history and organized on the principles of Plato's Republic, which turned out not to work so well in practice. In The Philosopher Kings the single original city had split into a dozen: five feuding ones on Thera and another eight on other islands where the inhabitants turned out to be preaching Christianity to Iron Age Greeks. In large part because of the anachronistic introduction of Christianity, all of the cities were relocated by Zeus to an uninhabited far-off planet in the 26th century, which the cities' inhabitants promptly named Plato.