I have a fantasy setting that is about as advanced as the late 15th to early 16th century. There are humans and many other sapient non-human species; humans are one of the only species to create large kingdoms and empires.
Some human rulers keep non-humans as exotic servants, slaves or part of private menageries to show off their wealth and power. Among the non-human species kept are trolls, humanoids descended from baboons. A male can be up to 8 feet tall with the proportional strength of a gorilla.
How would their masters prevent their troll slaves from escaping or rebelling? A troll could snap a human spine in half with no effort.
Trolls are as intelligent as humans and their societies range from hunter-gatherer tribes of less than 50 people to small agricultural villages with a population of 200-300.
The scenario I'm thinking of is a human noble keeping a small group of less than 10 trolls as part of a private menagerie/servants to show off. As for magical means of control; magic is very rare in this setting and the average person has no knowledge of how to use magic.