The Tibetan Empire beginning in 600CE lasted untill 850CE. In this period we see a struggle over the Tarim basin between the Tibetans, the Chinese, and a Mongolic-speaking people called the Aza.
In the book “Army of Tang China” by Karl Heinz Ranitzsch It describes the Tibetan army the Tang Chinese fought against: “The men and horses all wear chain armour. It’s workmanship is extremely fine. It envelops them completely, leaving openings only for the two eyes. Thus strong bows and sharp swords cannot harm them. When they do battle, they must dismount and array themselves in ranks. When one dies another takes his place. To the end, they are not willing to retreat. Their lances are longer and thinner than those in China. Their archery is weak but their armour is strong. The men always use swords, when they are not at war they still go about carrying swords.”
Arab sources also refer of the Tibetan infantry. From another chapter in a battle where the Uighurs allied with Chinese to fight the Tibetans.
“The Uighurs considered themselves more of a match for the cumbersome Tibetan cavalry, the Chinese infantry was equipped with crossbows with leather flighted arrows and with longbows whose steel tipped arrows could pierce the Tibetan armor.The Tibetan infantry were the main threat ,Heavily armed encased in armor they were known for their bravery under attack.But the Tibetan army was also reinforced by Turkic soldiers who were excellent cavalrymen.The Tibetan army was waiting for the allied army under Beshbaliq.The Chinese and Uighurs could make no headway against the Tibetans and as the battle progressed they became weak and dispirited,then at last the Tibetan lines begun to advance a grey ironclad mass of Tibetan infantry rolled forward relentlessly routing the enemy”. There was an exhibition of Tibetan arms and armours in New York last summer