Longyou Caves (龙游石窟)

Peer-reviewed confirmed geology: Cretaceous argillaceous siltstone, high mechanical strength, responsible for structural stability over an estimated ~2,000 years. Li et al. (Tunnelling and Underground Space Technology, 2009, DOI 10.1016/j.tust.2008.08.003) describe 24 caves, sloped roofs (~45°), ceilings parallel to the bedding planes — a structure naturally exploiting planes of weakness.

Striations: regular bands ~60 cm wide, marks at ~60° to the cave's axis, consistent across all walls and ceilings. Yue et al. (Frontiers of Architecture and Civil Engineering in China, 2010, DOI 10.1007/s11709-010-0018-1) propose that these marks are consistent with a hand tool (V-shaped chisel), with no evidence of machinery. Li et al. (CRC Press, 2015, DOI 10.1201/b19169-20) measure the weathering rates of the striations to establish a lower bound for age — not an absolute date.

Dating: no peer-reviewed English-language publication with radiometric dating (C14, OSL, U/Th) has been found. The 'about 2,000 years / Han' estimate rests on ceramic sherds in indirect archaeological context — with no published chain of evidence. Li et al. (2009) put forward this working hypothesis without validating it instrumentally.

Excavated volume estimated at ~1,000,000 m³: a figure circulating in the technical literature (Li et al. 2009) but not measured archaeologically in the strict sense. To be used with the qualifier 'estimated'.

Absence of any mention in the Chinese historical annals: confirmed by all academic sources consulted. Neither the Shiji, nor the Hanshu, nor the local Quzhou chronicles list these caves. This fact itself is documented peer-reviewed (Li et al. 2009, Yue et al. 2010).