The Phra Nang Chamathewi Monument is located within the old city wall in the southwest corner. The monument is to Queen Chamathewi, first ruler of the Hariphunchai kingdom.

Acording to mythology, Phra Nang Chamathewi was born in Lamphun but adopted by the Lawo Court (Lopburi), a leading power at that time. Matters came to a head when she was still in her teens as a result of an arranged marriage to a local ruler. Showing her allegiance to the Mon people in Lamphun who were suffering under Lawo rule, she rebelled, raising an army successfully gaining independence from Lawo in 653. She entered Lamphun and was crowned queen setting up the new kingdom of Hariphunchai in 663.