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 enpun . 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 located in Goseong County, South Gyeongsang Ancient Tomb Group, is the Zenpokoenfun.

Kofun are megalithic tombs or tumuli in Northeast Asia. Kofun were mainly constructed in the Japanese archipelago between the middle of the 3rd century to the early 7th century CE.