The first military conflict between China and Tibet occurred in 638. In the early 7th century, the westward conquests of the Tang dynasty brought it into contact with the rising Tibetan Empire. When Emperor Taizong of Tang refused a marriage alliance, the Tibetan emperor Songtsen Gampo sent an army to attack the Chinese frontier city of Songzhou (松州, in modern Sichuan). After a Tang army inflicted heavy casualties on the Tibetans in a night-time attack, Songtsen Gampo withdrew. He sent emissaries and tributes to Chang'an to apologize, and to again request marriage. Taizong decided to give Songtsen Gampo a distant niece, Princess Wencheng, in marriage. The peace held for the remainder of the reigns of Taizong and Songtsen Gampo, although Tibet would pose major military threats for most of the rest of the Tang period.