The lingam is one of the oldest symbols of life and fertility in South Asia. While lingams were probably part of the religious lives of even the earliest peoples of the region, they came to be identified with the classical Hindu god Shiva. Shiva is a god of ambiguities and opposites: he lives a happy domestic life with his wife, the goddess Parvati, and his two sons, and he lives another life as a forest-dwelling ascetic surrounded by animals.
For a Hindu visitor to the temple, this four-faced lingam communicates the mystery of Shiva's many aspects. It would have been housed in a small enclosure in the inner sanctum of the temple, and as the residue of paint suggests, brightly decorated. His third eye is visible on all of his foreheads, and shows his ability to see in all four cosmic directions. Hindu and Buddhist iconography has co-existed for over two thousand years in Nepal, and a Nepali worshipper would see the same four-fold faces and eyes around the tops of Buddhist stupas.