Dropping one more piece of information in case anyone isn't aware of it yet. The battlefield has been decided to be roughly 50km in radius (that is 100 km diameter) centered around the basilica. i.e.: it's a relatively sized piece of countryside terrain turned supernatural graveyard.

Just for comparison's sake, at the standard speed of the sound, Mach 01 (roughly 1250km/h), it takes about two and a half minutes to go from te basilica to anywhere in the battlefield and vice-versa. Use this when you consider how fast you can travel around the area, specially for the people that can fly.