As this is the first gateway of both Earth and Heaven, and as the sun first rises in this quarter, this is called the East.
पूर्वमेतत् कृतं द्वारं पृथिव्या भुवनस्य च। सूर्यस्योदयनं चैव पूर्वा ह्येषा दिगुच्यते॥