Long vowels

A long vowel is a vowel which occupies two moras, in other words two kana. For example, the ō in Tōkyō is a long vowel. Long o and long u, written ō and ū in rōmaji and おう and うう in kana, are very common in Japanese, especially in on'yomi of Chinese derived words. In gairaigo and native Japanese words, there are also often long i as well as long a vowels. In rōmaji these are not written with a macron, for example shiitake is usually just written with two 'i's rather than an i with a macron. In katakana they are usually written with a chōon mark.