What does Montale mean when he refers to life consisting of 'following a wall with shards of bottles embedded in the top'?

To understand this quote it is important for us to remember the fundamental theme of negativity that runs throughout all of Montale's poetry. As we have seen in other poems, Montale suggests that there is a negative and doomed relationship between nature and humanity, due to modernisation and the ageing process. As a result, we have seen that Montale falls into a form of existential angst (briefly run through history of existentialism).With that in mind, we can now analyse the specific line. It may be useful to visualise the image of a wall entrapping you with shards embedded in the top. What Montale is referring to here is that very existential trap, but perhaps one with a peak and hence the possibility of escaping. However, with the image of the glass bottles shards we can see that such an escape will be inevitably painful, fatal or perhaps impossible for many people. As a result, looking back on the third line of this stanza, Montale believes life is consistently attached to "travaglio" (torment), such pain underlined by the phonetic features of this stanza, which is filled with hard t, z and c sounds. This reflects the harsh bitterness of life.