Fire is the medium through which the rule of tying all the goddesses in the form of fire as witnesses has been told in the religious texts.
According to Vedic rules, there is a rule to take four rounds before marriage. In the first three rounds the bride walks ahead while in the fourth round the groom walks ahead.
There Mangalsutra is even more important than Saptapadi. It is considered mandatory to have a garland of black pearls, a peacock feather and a locket in Mangalsutra.
The yellow part of the Mangalsutra symbolizes Goddess Parvati and the black part symbolizes Lord Shiva. After marriage, Lord Shiva and Parvati protect the bride.
At the time of marriage, the act of applying vermilion to the bride by the groom, wishing for a long life, applies vermilion in the demand of life as a symbol of being married.
It also protects the marma place from external bad effects. Women are advised in the scriptures to apply vermilion in the maang to remove bad doshas.