Discuss the symbolic significance of the Marabar Caves in A Passage to India

The symbolic significance of the 'Marabar Caves' in 'A Passage to India' of E.M Forster is very complex. 

In fact, the central point of the novel is the nightmarish experience of two English women , Mrs. Moore and Adela Quested in these Caves.  Mrs. Moore is destroyed both spiritually and physically ; Adela is driven to the brink of madness . Aziz is ruined and the passage to India which the two women have undertaken seems to save failed .

The 'Marabar Caves' are a mystery and so is India . They are extraordinary but why they are so is left unexplained.  We are told that the Marabar Caves were pre-historic. They pre-dated Islam, Christianity and even Hinduism,  which are the oldest religion in the world . They stand for chaos,  darkness and evils. The westerners were brought face to face with the reality of evil that forms a part of the universe.

The horrible experiences of Mrs. Moore and Adela Quested posed a challenge to the comfortable Christianity of the former and the rationalistic liberal claims of the other.  Mrs.Moore shocked in the very first cave ,was a mystic who had wished to communicate with God looking on this communion as something beautiful . The dark and empty caves revealed the hollowness of life where nothing mattered.  The vacuum and littleness of the caves produced an echo that was frightening.

In a moment , Mrs. Moore finds herself becoming completely uninterested in everyone around her,including her children.  Even the Christian God,  on whose love and understanding she had based her entire existence , becomes completely meaningless.

The same echo which destroyed Mrs. Moore physically  destroys Adela Quested psychologically in the next scene when she visits the caves with Dr. Aziz.The darkness of the cave destroys her balance of  mind so much that she even gets a hallucination that someone is trying to rape her. She goesnad with horror and, in sheer shock and exhaustion she rushes down the caves , goes to the nearest police station , hysterically accusing Aziz of trying to rape her. Her delusion starts the machinery that will send Aziz to jail and shatter the peace of Chandrapore.

Thus the incident at "Marabar Caves ' is merely an echo , a kind of monotonous meaningless "bou-oum " sound.But by hearing this echo in the caves,  two British women unwilling and against their best intentions , have released Evil which spreads everywhere.