Final answer:
The National Mall in Washington D.C. is designed in the Neoclassical style, capturing the aesthetic of ancient Greek and Roman architecture and reflecting America's admiration for these civilizations.
Step-by-step explanation:
The style in which the National Mall in Washington D.C. is designed is Neoclassical. This architectural style seeks to capture the elegance, simplicity, and symmetry of ancient Greek and Roman buildings. Notably, Neoclassicism was a significant force in academic art through the 19th century and was seen as a constant antithesis to Romanticism or Gothic revivals. The U.S. Capitol building, which is situated at the eastern end of the National Mall, is an outstanding example of Classical Revival architecture in the United States, symbolizing the political ideals of the Romans and Greeks. The preference for Neoclassical architecture during America's formative years reflected widespread admiration for Greek democracy and Roman law.