Commentary Inf XXIII 133-138

Virgil's question to Catalano (and Loderingo) receives this devastating answer: he has been fooled by Malacoda; all the bridges connecting the fifth and sixth 'valleys' are down.

The noun ruina, describing the fallen rock that will allow an exit from this bolgia, connects to the same word used with the same meaning in [Inf XII 4] and [Inf XII 34]. And see C.Inf.V.34 for the difficult problem of its meaning in that verse.