What's the earliest music you enjoy?

Fun question for a Friday: What's the earliest music (in terms of date of composition or publication) that you enjoy listening to?

I'll go first and say that the earliest composition in my collection is Perotin's Viderunt Omnes from (according to wikipedia) 1198. It is very, very austere and not for the faint of heart, but is definitely fitting for a cold Winter morning!

What's yours? This is half contest and half me wanting to look deeper into the foundations of the music we know and love today, so I will definitely be checking out anything y'all care to mention :)