The Japanese educational system, and particularly the strait gate/narrow way that leadeth from high school to college, still demands of its victims a great deal of memorization. The educational theory here is that people whose heads are filled with specific facts of grave importance can go on to use these facts as a framework for integrating new information and developing a deeper understanding of the world. The reality, of course, is that you end up with a bunch of 18-year-olds cramming their minds full of nonsense mnemonics designed to last until the college exams are over.

The most widespread of these mnemonics are the goroawase for memorizing numbers, and the most widely beloved of those are the ones used in history class to remember important years. The canonical history goroawase is ii kuni tsukurō ["let's found a good country"], Kamakura bakufu: i-i-ku-ni = 1-1-9-2, i.e. 1192 CE, the year the Kamakura shogunate officially began with the shogunation of Minamoto no Yoritomo 源頼朝. Ii kuni tsukurō is canonical for a few reasons: it's about an important event that students will read about multiple times; it's whimsical without being completely nonsensical or surreal; it's related to the event rather than just being a bunch of words that happen to add up to the right year.

You can find long lists quite pretty easily (in Japanese, natch); here are a few others I like.

• Romio mo ikimasu, daiikkai kentōshi = "Romeo goes too: first mission to the Tang" (ro-mi-o = 630)
• Nanto rippa na Heijō-kyō = "How marvelous is this Heijō-kyō!" (nan-to = 710)
• Naku yo, uguisu, Heian-kyō = "The warbler cries: Heian-kyō" (na-ku-yo = 794) [This one has variants like Haku yo, uguisu ("The warbler vomits") for 894 when the missions to the Tang were stopped, etc.]
• Ii munage, Taira no Kiyomori = "Great chest hair, Taira no Kiyomori 平清盛 [becomes Chancellor of the Realm] (i-i-mu-na = 1167)
• Iroiro sankyū, Porutogaru = "Thanks for everything, Portugal" (for the closing of Japan's ports to Portuguese ships; i-ro-san-kyū = 1639)
• Yakko-san mo bikkuri, Perii no kurofune = "Even the servants were shocked at Perry's black ships" (ya-go-san = 853; the initial "1" you just remember)