Zenpokoenfun is an architectural model of Japanese ancient tombs (Kofun), which consists of a square front part (前方部) and a circular back part (後円部). The part connecting the two is called the middle part (くびれ部), which looks like a keyhole when viewed from above. Therefore, they are also called keyhole-shaped mounds in English, and in Korean, they are called long drum tombs (장고분) due to their resemblance to Janggu, and it is also a form of the Kofun that appeared earlier in the Kofun period along with the circular-type (Enfun). Generally, large Kofun are front and rear circular tombs, widely distributed in Honshu, Shikoku, and Kyushu with Gokishichidō as the center. Among them, the largest front and rear circular tomb in Japan are the Mozu Tombs with a total length of 525 meters. In addition to Japan, there are also the front and rear circular tombs in South Korea, as well as the front and rear circular tombs in Chosan County Ancient Tomb Group and Chasong County Ancient Tomb Group located in North Korea. In addition, Korean archaeologist Jiang Renqiu believes that the Songhe Dong No. 1 Tomb (Wuyishan Mountain Kofun) located in Goseong County, South Gyeongsang Ancient Tomb Group, is the Zenpokoenfun.
At first, Zenpokoenfun did not have a specific name, but were named after objects that were around the people during that era. Therefore, they were also known as Chezun, Yaozi, Chajiu, Calabash, Piaozhong, and Erzi Tombs. Chezun refers to the front and back circular parts of Kofun, which are named after cars. Yaozi Tomb is named after the fact that when viewed from the side, it looks like half of the lying Yaozi, Chajiu Tomb is named after the two or three layers of the back circle that look like a teacup and is also known as the teacup tomb and the cup-shaped tomb. The cup-shaped tomb, refers to the shape of the front and back circular tombs, which is like half of a gourd buried in the soil. Erzi Tomb, also known as the Erzi Tomb and Gemini Tomb, refers to the front and back circular tombs with similar heights between the front and back parts.