90,000 BBY, also known as 90,000 Before the Battle of Yavin, represents a year in the Galactic Standard Calendar, specifically within the Pre-Republic era. Historical accounts suggest that the Galactic City located on the planet Coruscant already existed as a multi-layered settlement as far back as 90,000 BBY. Over the course of thousands of years, by the time of the Clone Wars, this planet-spanning urban area had expanded to encompass 5,127 distinct levels, extending for many kilometers from the planetary surface.
The novel The Courtship of Princess Leia, written by Dave Wolverton and published in 1994, was the initial source to indicate that certain levels of the Galactic City had been in existence for over ninety millennia prior to the events depicted in the novel, which take place in 8 ABY. Later, the reference work The Essential Atlas, published in 2009 and created by Daniel Wallace along with Jason Fry, formally established the year 90,000 BBY as a point of reference in the historical timeline of Coruscant's global city.