* Early Forms: Katakana's roots can be traced back to the 8th century, when Buddhist monks began using abbreviated forms of Chinese characters (kanji) for phonetic notation in their Buddhist scriptures. These abbreviated forms were called "manyogana" (manyo-gana).
* Development: Over the centuries, these abbreviated forms continued to be used and developed. The term "katakana" itself emerged around the 10th century to distinguish these abbreviated characters from another type of phonetic notation called "hiragana."
* Standardization: While katakana existed for centuries, it wasn't until the 16th-17th centuries that the system became standardized and gained widespread use in writing.
So, while there isn't a definitive "invention" date, katakana's origins can be traced back to the 8th century with its full development and standardization occurring much later.