Context: The city was originally built on a hilly peninsula surrounded by the River Aare, but outgrew natural boundaries by the 19th century. A number of bridges have been built to allow the city to expand beyond the Aare.

Question: What peninsula is Bern located on?
Answer: Aare

Question: What was built to help Bern grow bigger than the peninula?
Answer: bridges

Question: What century did Bern outgrow the peninsula?
Answer: 19th century