"The blood shall be a sign for you on the houses where you live; and when I see the blood I will pass over you, and no plague will befall you to destroy you when I strike the land..."
A battlefield is likely to be centered around a landmark such as a shrine, a farmhouse, an army outpost or some other strategically important location in a zone's RvR area. Players from each Realm will be able to engage in open world RvR combat in battlefields.
Winning a zone in this so-called open RvR is archieved by leveling your own keep until you have siege weapons and conquering the enemy keep afterwards.
Before 1.4, winning the zones was isntead archieved by gathering victory points, until a specific amount was reached or capturing all objectives for a specific, long time.