Final answer:
Building walls in ancient times was difficult due to the need for substantial manpower, environmental conditions suitable for materials like rammed earth, and technological constraints that limited the size of structural openings without causing collapse.
Step-by-step explanation:
The conditions that made walls difficult to build encompassed a range of challenges. Natural material availability and environmental conditions heavily influenced construction methods. Building with rammed earth was a sturdy option but required significant manpower and specific environmental conditions to ensure solidity. Large structures, such as city walls or the early sections of the Great Wall of China, required a framework of wooden frames filled with small rocks and dirt and then tamped down to form thick, sturdy walls. Limitations in construction technology of the period meant that large windows or doors compromised the integrity of load-bearing walls, risking structural failure. The labor force, often consisting of farmers and specialized artisans, faced tremendous tasks such as creating immense defensive walls for populated cities like Chang'an or constructing intricate structures like the Forbidden City, with its wall systems and open roofing. Furthermore, conditions at construction sites, such as narrow valleys, unstable geological foundations as seen in the Vajont Dam incident, or the need to transport materials over great distances during specific seasons, added to the complexity of building walls.