The traditional Mongolian script, also known as the Hudum Mongol bichig, was the first writing system created specifically for the Mongolian language, and was the most widespread until the introduction of Cyrillic in 1946. Wikipedia

Vertically written traditional Mongolian script Wikidata

The first of many writing systems created for the Mongolian language, and the most successful until the introduction of Cyrillic to Mongolia in 1946. With minor modification, it is used in Inner Mongolia in China to this day to write Mongolian and the Evenk language. OmegaWiki