According to ancient mythology, Lord Brahma performed Das (ten) Ashwamedh sacrifices here and a bath here confers the benefits of ten Ashwamedh. Of all the Ghats along the Bank of the Ganges, this is the most popular Ghat and is the hub of pilgrims morning and evening. It is also know as “Brahma Dwar” (Door Step of Brahma) and its old name is Rudrasarovar or Ghoraghat and is one of the five ‘Panchteerthas’ of Kashi. After coming of the Ganges the Rudrasarovar disappeared and this site continued to be regarded as the prominent place of pilgrimage in Kashi and come to be know as Prayag Rajghat. Among the Ghats of Varanasi there are three which are very prominent and of these three Dashashwamdh Ghat is of the prime importance. The Karmas done here not destroyed and remain forever (akshya). The present ghat was built in 1748 by Peshwa Balaji Bajirao. Ganga Aarti is performed daily at Morning and in the evening.
Source: Uttar Pradesh tourism