In which historical period did the form of Beijing begin to take shape?

The correct choice is the Ming dynasty, as this period marks a significant phase in the formation of Beijing’s layout and architectural style. During the Ming dynasty, specifically in the early 15th century under the Yongle Emperor, Beijing was established as the capital of China. This led to extensive urban planning efforts, resulting in the construction of monumental structures such as the Forbidden City and the city’s walls, which were designed with a focus on axial symmetry and hierarchical organization.

The urban design principles laid down during the Ming dynasty emphasized a structured and formal layout, influencing the overall development of the city and its cultural landscape for centuries to come. The strategic planning and architectural advancements made in Beijing during this era are crucial in understanding the historical significance and identity of the city today.

Other historical periods, while important in their own rights, did not have the same level of influence on the city’s form as the Ming dynasty did. For example, the Qin dynasty helped unify China but did not specifically shape Beijing's character. The Tang and Song dynasties were also pivotal in Chinese history but primarily influenced other regions and developments rather than the specific form of Beijing that we recognize today.