Tibetan forces, apparently commanded by Songtsän Gampo himself, raid the Tang frontier city of Songzhou (modern Songpan County in Sichuan) in the fall of 638, but meanwhile send emissaries to the Tang capital Chang'an, again offering tributes and declaring that they are intending to welcome a princess.

The size of Songtsän Gampo’s army is given as one hundred thousand by Tibetan sources and over two hundred thousand by Chinese sources.

They defeat a force sent against them by the Songzhou governor Han Wei.

According to the Chinese annals, Taizong respondd by commissioning the general Hou Junji to command an army, assisted by the generals Zhishi Sili, Niu Jinda and Liu Jian.

Led by Niu, the Tang army inflicts heavy casualties on the Tibetans in a surprise night attack.

Alarmed, Songtsän Gampo withdraws, sent emissaries and tributes to Chang'an to apologize and to again request marriage.

Emperor Taizong agrees this time.

However, no further action will be taken to carry out the marriage for about two years.