subdivides these knives into Three Character Knives (三字刀), Four Character Knives (四字刀), Five Character Knives (五字刀), and Six Character Knives (六字刀). It is believed that of all these categories that the Four Character Knives are the oldest and that they were introduced sometime early during the Spring and Autumn Period. The Five Character Knives began to be produced in the late Spring and Autumn Period. The Three Character Knives are found to have begun circulating during the early to middle Warring States Period. While earliest form of knife money circulated in the State of Qi, knife money would later spread to the States of Yan and Zhao. All types of Qi knife money are considered to be rare in the modern era. Three Character Knives Some Three Character Knives (三字刀) bear the inscription "Qi fa hua" (齊法化, "Qi Legal Money"). Five Character Knives Qi knives with five character inscriptions produced in the city of Jimo (present-day Pingdu, Shandong had the inscription "Ji mo zhi fa hua" (即墨之法化, "Jimo Legal Money"). Qi knives with five character inscriptions produced in the city of Anyang (situated just east of what is now Caoxian, Shandong) had the inscription "An yang zhi fa hua" (安陽之法化, "Anyang Legal Money"). Six Character Knives The Six Character Knives from the State of Qi were issued as a type of "commemorative coin" (). Six Character Knives tend to be quite large and thick, they were usually finely cast and made from quality bronze, and their inscriptions tend to display exquisite Chinese calligraphy. Six Character Knives are typically between 18.2 and 18.5 centimeters in length, between 2.8 and 2.9 centimeters in width, and their weight tends to be 45.5 and 50.9 grams. One of the earlier commemorative issues of the Six Character Knives is to commemorate when Duke Tai of Tian Qi was formally recognised as the ruler of the State of Qi in the year 386 BC. This is the first known commemorative coin in the history of China and its inscription is written in an ancient Chinese script which today has become difficult to decipher. The inscription is believed to be "qi zao bang chang fa huo" () which translates into English as "Qi, establish state long, legal money". However, other than this reading there are alternative interpretations of the inscription of this Six Character Knife. There are some experts who believe that the inscription doesn't read "齊造邦長法化",