I want to know the answer to the following question:
What is the earliest that they kept live bears in the Bärengraben?
All the background I'm provided with is that "As a result of the find of the Bern zinc tablet in the 1980s, it is now more common to assume that the city was named after a pre-existing toponym of Celtic origin, possibly *berna "cleft".". Is that enough to answer the question?
Answer: no