Occasionally, the fertility goddess or guardian deity can be the spirit of a historical figure. This practice has roots in ancient times: as early as the Sangam period, hero stones ("natukal/viragal" in Tamil, "veeragalu" in Kannada), stones erected to honour those men who laid down their lives for the village, were worshipped and propitiated. Similar to hero stones, sati stones honour women who sacrificed their life, especially for chastity and purity. The early Tamil poem "Tolkappiyam" gives a six-stage guide to the erection of such a stone, from selection of a suitable stone until the institution of formal worship. In time, many of these spirits have merged into or become the local guardian deity. Examples of deified heroes include Madurai Veeran (from Madurai) and Kathavarayan (from Thanjavur). Oftentimes, these heroes are found as attendants to Ayyanar or a village goddess, especially in Tamil Nadu. The Paanchamman temples in north Tamil Nadu were built to worship widows who underwent Sati. Often, the deities are spirits who suffered injustice in their lives or deaths and must be propitiated to prevent their spirit from affecting the village. Several couples who have lost their lives due to caste animosity are worshipped as deities in several villages. Kannaki Amman is Kannagi from the "Silappadikaram", whose husband was unjustly killed by the Pandyan king, is another widely-worshipped deity of this category. The Maachani Amman temple at Pollachi was built to worship a young girl who was killed by a Kongu king for unknowingly eating a mango from his garden. Oftentimes female spirits are merged into the main fertility goddess, or are venerated as one of her attendants.