## 4 Discussion
### Geographic Context Controlling the Spatial-Temporal Distribution
#### 4.1.1 Topographic Feature in Relation to Prehistoric Settlements  
The elevation of the middle and lower reaches of the Yuanjiang River is closely linked to the region's terrain and landforms. The middle reaches are characterized by inter-mountain basin landforms with altitudes between 100 and 500 m, while the lower reaches primarily feature flat plain landforms below 100 m. Both types of terrain consist of low, flat, and open areas, which have played a significant role in human settlement and cultural development. Statistical analyses using ArcGIS software highlighted distinct patterns in the distribution of archaeological sites across various elevations (see Figure 4a). The distribution of Paleolithic sites was concentrated in relatively flat and open regions around 100-500 m above sea level. In contrast, there were fewer sites located below 100 m [29]. During the Neolithic period, archaeological sites became more widely distributed, with many \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**River** & **Terrace Level** & **Height/m** & **Height/m** & **Age/ka** \\  & & **a.s.l.** & **a.r.l.** & **Age/ka** \\ \hline \multirow{4}{*}{Middle-lower reaches of the the Lishui River [48]} & T\({}_{4}\) in Huzhuashan site & 95 & 63 & 500 \(\pm\) 50 (ESR) \\  & T\({}_{3}\) in Houerpo site & 80 & 40 & 200 \(\pm\) 15 (ESR) \\  & T\({}_{2}\) in the Wuyashan site & 55 & 22 & 57.8 \(\pm\) 5.0 (ESR) \\  & T\({}_{1}\) in Yanerdong site & 40 & 13 & 20-30 \(\pm\) 2.0 (ESR) \\ \hline \multirow{4}{*}{Yuanjiang River [35; 41]} & T\({}_{6}\) & – & 120–140 & Early Early Pleistocene \\  & T\({}_{5}\) & – & 80–87 & Late Early Pleistocene \\  & T\({}_{4}\) & – & 78 & Early Middle Pleistocene \\  & T\({}_{3}\) & – & 38 & Middle Middle Pleistocene \\  & T\({}_{2}\) & – & 16 & Late Middle Pleistocene \\  & T\({}_{1}\) & – & 10 & Late Pleistocene \\ \hline \multirow{4}{*}{Yuanjiang River (our study)} & T\({}_{5}\) & – & 80–110 & Late Early Pleistocene \\  & T\({}_{4}\) & – & 71–82 & 470 \(\pm\) 47 (ESR) \\ \cline{1-1}  & T\({}_{3}\) & – & 34–46 & 151–305 \(\pm\) 20 (ESR) \\ \cline{1-1}  & T\({}_{2}\) & – & 14–21 & 56–58 \(\pm\) 5.0 (ESR) \\ \cline{1-1}  & T\({}_{1}\) & – & 8–14 & 9–31 \(\pm\) 2.0 (ESR) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._found below 500 m. This broader distribution reflected the rapid cultural development occurring in the lower reaches of the Yuanjiang River, resulting in a significant number of sites below 100 m. By the Shang and Zhou dynasties, patterns of human habitation evolved, as the number of archaeological sites above 500 m began to increase (Figure 4a). This shift indicated that communities were moving beyond low-lying areas near riverine water sources, motivated largely by the need to avoid floods and other environmental hazards. As agricultural practices expanded, there was a growing reliance on stable living conditions, allowing populations to settle at higher altitudes to mitigate flooding risks [19; 25; 32]. In summary, the impact of altitude on ancient cultural changes was particularly evident in the middle reaches of the Yuanjiang River, especially between 100 and 500 m. The site distribution from the Paleolithic period suggests a preference for higher altitudes, driven by the challenges that early humans faced in adapting to their environment and the necessity of finding safer, flood-resistant locations. From the Neolithic to the Shang and Zhou dynasties, the altitude distribution of ancient cultural sites remained relatively stable, with a predominant concentration below 300 m. This stability implied that human habitation patterns in the middle reaches have been fairly consistent since the Neolithic, offering valuable insights into site selection for ancient communities [19; 25]. Although the research area spans nearly 100,000 square kilometers, there is an error of approximately 100 m in the location data on the cultural relic map. However, the integration of 90-m resolution SRTM data is sufficient to capture the macroscopic geometric features of the site.