Why is a mound of cow dung made on Govardhan Puja?

A mound of cow dung is made on Govardhan Puja to symbolise Govardhan mountain that Lord Krishna lifted on his little finger to protect the people. It's made from cow dung, as Goddess Mahalakshmi, the presiding deity of wealth, is believed to reside in cow dung. Fresh cow dung is considered a natural antibacterial and destroyer of negative energy.