From Plato's Critias:
“Let me begin by observing first of all, that nine thousand was the sum of years which had elapsed since the war which was said to have taken place between those who dwelt outside the pillars of Heracles and all who dwelt within them; this war I am going to describe. ”
Excerpt From: Plato. “Critias.” iBooks. https://itunes.apple.com/us/book/critias/id498662802?mt=11
This is a second reference to the time when Atlantis supposedly existed. 9000 years before Solon's time is roughly equal to 11600 years before our time.