Through the twentieth century, scholars knew that Goguryeo, Baekje, and Silla each had a distinct monastery plan, that each plan was constructed subsequently in Asuka, Japan, and that only the Baekje plan could be documented earlier in China than in Korea. In the first decade of the twenty-first century, excavation confirmed an earlier Chinese source for the Silla plan. Sources of the Goguryeo plan, with a towering pagoda and three Buddha halls, have remained elusive. This paper examines possible Chinese sources. The new evidence comes from the Pingcheng capital, today Datong, where the Northern Wei dynasty moved in 398. Already in 1981, the remains of Siyuan Buddhist Monastery, built in 479 in hills outside Pingcheng, suggested a central pagoda and least one additional hall. Yet Buddhism had come to Goguryeo in 372; and its oldest monasteries are in Pyongyang, where the capital moved in 427. The newly-identified Pingcheng monasteries are above Yungang caves 5-6 and 39. If the monasteries are contemporary to the caves beneath them, they date to the 470s. Evidence up to the year 2020 will be presented and evaluated to assess if there is a version of the Goguryeo monastery plan that predates the year 427. The paper will also briefly explore the implications of monasteries with freestanding architecture above Buddhist cave-temples.