The Qin Dynasty's Fen City, as the ancient capital of the Qin state, is believed to be located in modern-day Xi'an, China. This conclusion is based on historical records and archaeological evidence that point to the region's significance during the Qin Dynasty.

The Qin Dynasty, which ruled China from 221 to 206 BCE, was known for its unification of the various states into a single empire. Fen City, as the capital of the Qin state before the unification, held great strategic and political importance. The city's location was crucial for the dynasty's control over the central plains of China, which facilitated the expansion and consolidation of the empire.

Archaeological excavations in the Xi'an area have uncovered remnants of ancient structures and artifacts that date back to the Qin Dynasty. The city's layout, with its grand palaces, fortresses, and other imperial buildings, aligns with historical descriptions of Fen City. Furthermore, the famous Terracotta Army, discovered near Xi'an, is believed to have been part of the defense system of Fen City, indicating its strategic importance.

Historical texts, such as the "Records of the Grand Historian" by Sima Qian, provide detailed accounts of the city's location and its role in the Qin Dynasty. These accounts, combined with archaeological findings, strongly suggest that Fen City is indeed located in modern Xi'an.

In conclusion, the Qin Dynasty's Fen City is widely believed to be situated in Xi'an, China, based on historical records, archaeological evidence, and textual references. The city's strategic location and its role as the capital of the Qin state further solidify this identification.