A Study on the Modular Layout Principles of Sui-Tang Luoyang Based on Compositional Proportions

Sui-Tang Luoyang was an international metropolis during the 7th–10th centuries, yet the layout principles that shaped its fundamental urban form have long remained undisclosed. This study takes the Danei as the benchmark and, based on the compositional proportions observed in the palace – imperial layout, combined with grid arrangement, identifies the modular relationships governing the entire capital. The research reveals that:(1) 24 zhang (70.56 m) served as the fundamental module not only for the Danei but also for the planning of the palace city, imperial city, and even the outer city.(2) Through the circle–square relationships embedded in compositional proportions such as 1:1, 5:7, 6:7 and 3:4, the entire capital achieved a symbolic expression of the cosmological concept "Round Heaven, Square Earth".Uncovering these modular layout principles will facilitate subsequent archaeological investigations and enhance the presentation and utilization of the heritage value of Sui-Tang Luoyang.