[Graeme Dice]

Originally posted by Boron:
Edit : is it enough to have a castle in a neighbor province or do you need to fully control the province ?

You need to control the province at the time that retreats are figured out, which is after battles near the end of the turn. A spell like ghost riders, which gives the province to independents until the beginning of the next turn, can prevent him from retreating successfully.

if i have 1 neighbor province but are besieged there and my harvester is ddiscovered and retreats does he retreat to the castle , or retreat to the province and sneak around there or does he have nowhere to retreat ?

All units can only retreat to neighbouring friendly provinces. Flying and stealth don't matter in this at all.