Current sales: Civ4, Civ5, Civ6 and Millennia
There are currently various Steam sales going on, most likely due to the recent Civ7 info. Civ4 is currently discounted by 85%. Civ5 is currently discounted by 75%. Civ6 is currently discounted by 90%. Millennia is currently discounted by 50% (see also thread here).