The History of Prayer Flag
In Tibetan, prayer flag is called lungta or windhorse (རླུང་རྟ་). Many of you think that lungta is the tradition of the Buddhists. However, it is not the case. Buddhism comes from India, but India does not have prayer flag. Some people did research on this. It seemed that prayer flag did not come from Tibet. Instead, it came from China. During the early dynasties of China, flag was usually used to represent a kingdom, village, or town. Symbols were usually imprinted on the flags such as horse, dragon, etc. A flag from a very early time was discovered to have the painting of dragon surrounding a horse. This flag was commonly used in the early time of China. It was called longma (龙马), where long (龙) means dragon, and ma (马) means horse. When this flag came to Tibet long was retained because Tibetans did not know an animal called 'dragon'. On the other hand, as Tibetan also had their own word for horse, that is ta (རྟ) the flag was called longta. The long that means dragon, later transformed into lung (རླུང) in Tibetan that means wind. This history was what someone has researched upon. It sounds quite logical because other than this story, there was no other account of lungta.
Then, how does the tradition of windhorse was converted as a Buddhist tradition? Buddhism came to Tibet around the 7th- 8th century. Many Tibetan cultures during the time were connected to the Bon culture and it was difficult for people to eradicate these longstanding culture and practices. The old tradition has to be retained in order for Buddhism to be able to assimilate. Otherwise, the Tibetans may not welcome Buddhism. Fortunately, all the masters who spreaded Buddhism were very skillful. They converted the local culture to suit Buddhism. This conversion also happened to prayer flag. These masters started to think of the best way to convert prayer flag into the Buddhist way. They chose a Buddhist sutra called Gyaltsen Tsenmo Pung Gyen (རྒྱལ་མཚན་རྩེ་མོའི་དཔུང་རྒྱན་), translated roughly as Ornament on the Top of the Victory Banner. It was believed that if you put this sutra on the tip of a banner, you would be able to fight all negative forces. This sutra was found in Mahayana tradition and it traced back to the Buddha's time when the Buddha went to Tushita heaven to preach and liberate His mother.
During that period, Indra was defeated by the Demigod Asuras. He seeked help from the Buddha. Buddha told him that if they were to fight, they would kill each other and perished. However, there was a way where he may win victory without fighting. Buddha then bestowed him the Sutra of Ornament on the Top of the Victory Banner. Buddha asked Indra to put the sutra on the top of the banner of the fighting pole before going for the war. Indra went for the battle prepared with the sutra. The asuras surrendered without fighting any battle.
Therefore, the Buddhist masters chose this sutra to be put on a prayer flag. In this way, the prayer flag became very meaningful although it does not originate from India. People started to erect prayer flags the way the Buddha instructed Indra to do. This is how prayer flag becomes popular in Tibet. Most of you perhaps hang prayer flag on your windows, which is good, but you have to understand. If you say that prayer flag is a Buddhist tradition, a Theravada monk may ask, "How come is it a Buddhist tradition?". You are not able to answer to this question without an understanding. But if you know, you will be able to explain that the Buddhism adapts this tradition to the Buddhist teaching.