The practice of sacrifice for Devi is as old as the oldest of Tamil Sangam texts itself, dating back to 300 BC ( the texts ) by some researchers.
Tholkappiyam mentions Indra , Varuna , Mayon ( Visnu) , Murugan and Kotravai ( Durga ) were each in charge of one type of environment, Murugan being the Lord of the Hills and Mountains you understand why most of his temples are on hills.
Kotravai ( Durga ) on the other hand was the Goddess of the forests, hence her worship and sacrificial practices were probably done there.
It is mentioned that the iconography of Shankhu and Chakra were added later on, which were not present earlier.
The warriors you see circled in the pictures are those who would sacrifice themselves to her for their land , when they were at war.
There were 2 methods , one was by self beheading and another was by Navakandam the act of 9 cuts on their body where they would bleed out.
These warriors were enshrined in the Murti together with the Devi for their supreme sacrifice.
The faith they had in their Goddess puts most of us so called Bhaktas to shame.