Final answer:
The most influential policy of the Qin Dynasty was the standardization of writing and measurements, which established a basis for unity and efficient governance. Centralized bureaucracy supported by Legalist principles also played a vital role in the dynasty's administration. The Great Wall, while significant, had a more defensive and symbolic role.
Step-by-step explanation:
The most influential policy of the Qin Dynasty is arguably the standardization of writing and measurements. This policy not only facilitated communication and trade within a vast empire but also laid the foundations for a unified Chinese cultural identity. The imposition of a uniform script and consistent weights and measures were crucial for creating an efficient and centralized administrative system. Furthermore, standardized coinage, although not fully achieved before the collapse of the Qin, was initiated. These standardized systems outlived the dynasty and were inherited by the subsequent Han Dynasty, which further developed them and maintained imperial unity. Another significant policy was the centralized bureaucracy bolstered by Legalist tenets. Qin Shi Huang reorganized the state, doing away with the feudal system, and appointed officials to govern provinces, which reduced the power of local aristocracies and subjugated them to the emperor. Appointed officials were evaluated on their performance and governed according to uniform laws, contributing to the dynasty's short-lived unification and control. The construction of the Great Wall was also a monumental effort to protect the empire from northern invaders and symbolized the empire's power and reach. However, while it was an impressive feat, the importance of the Great Wall was more defensive and symbolic compared to the broad-reaching domestic impacts of writing, measurement standardization, and centralized governance.