How were noble prisoners treated during medieval times and in the Renaissance? Good and well fed or stuffed in a dark hole. I am asking about both periods because I know that some were allowed to move around freely and were only held by oath in captivity. What confuses me is the case of the earl of Bothweel who died held in a hole in the ground at the end of the 16th century.
It's too complicated a question to give a definitive answer.
It really depends who you were. Generally if you were a noble you were usually treated okay. Even applied to the way Muslims treated Christians. Saladin captured nobles fighting him in the crusade and treated them fine.
Normally if you were from another country and captured by the people your fighting they will let you live/treat you well. The Habsburg did this with Francois I of France after fighting off his forces in Italy. However if you were a threat to their rule (illegitimate heir, usurper etc) you were normally treated much worse and/or killed. It really depends on the context but chivalry between knights and nobility did exist.
The reason they often kept them alive was because they wanted a ransom. So they would extort the party for the same return of their noble/monarch. It was self interest to a large extent.