The article states that they likely built neither because nobody wants to be fighting for their life 1:1 on a dank staircase with poor visibility. It's actually

The article states that they likely built neither because nobody wants to be fighting for their life 1:1 on a dank staircase with poor visibility. It's actually the much more logical option. Even if attackers are in the stairwell, why wouldn't you retreat to the top where you can accumulate real advantages?