Vault 5

Vault 5 is where the Arena is located, and is one of the many Vaults built by Vault-Tec as part of their secret social experiment. The experiment was meant to test how the populace can handle numerous intentionally designed stress scenarios - many of them quite dangerous, if not outright lethal, to the inhabitants of the Vaults.

The only source of information about the Vault comes from the recordings made by Nicolaus Ainsworth, the Overseer. From them, we can learn that the Vault was initially occupied by over 200 people. Once the Vault door was closed, the control panel connected to it stopped responding, making the inhabitants effectively trapped inside. According to the orders from Vault-Tec given to Nicolaus, every night someone had to go inside the Arena, or else everyone would be irradiated to death.

This revelation induced a major outburst of panic, which Nicolaus and his wife Emily desperately tried to contain. After a long discussion, everyone concluded that whether they like it or not, they still have to send someone inside. A person named Taylor is mentioned as being the first to enter the Arena. Alas, they perished on Night 1.

The situation didn't go any better from there. Although Nicolaus and other inhabitants tried everything to stop this, they still had to send someone inside every night. At one point they attempted to refuse to do so, wanting to test out the theory that the radiation mentioned in Vault-Tec's orders is a lie. However, they learned that it was indeed true when the Vault was swiftly filled with deadly radiation. They had to quickly send another person inside, thus stopping the outburst of radiation.

The next-to-last message skips forward in time quite a bit, and has Emily argue with Nicolaus about the ongoing, depressing process of everyone dying one by one; sometimes not even from the Arena itself, but either from their attempts to escape, or from committing suicide when they couldn't handle it anymore. Emily decides to go inside herself, not wanting to wait until she's the last person left alive.

The last message has Nicolaus lament how he's the last person remaining, and that he still has to go inside the Arena. This makes it clear that all of the original inhabitants of the Vault eventually perished inside its walls.

Not much else is known about the Vault. No information is available about what lied inside the Vault, other than the Arena and the Reward Room. It is unknown whether the Vault was expected to have the inhabitants eventually succeed, or whether it was doomed to fail from the start.

Known inhabitants of the Vault

 * Nicolaus Ainsworth - The Overseer. Was the last person to enter the Arena.
 * Emily Ainsworth - The wife of the Overseer. Entered the Arena when there were about 30 people left alive. She presumably perished inside.
 * Taylor - The first person to go inside the Arena. Died on Night 1.
 * Jonathan - The second person to go inside. Died on Night 2.
 * Anthony - Another person who went inside. Died on Night 1.
 * Milo - Next-to-last person to enter the Arena. Died on Night 1.