However , due to lack of funds or resources , oft - interrupted construction , and the British attack on Washington during the War of 1812 , work on the rotunda did not begin until 1818 .
Thornton had first conceived the idea of a central rotunda .
Due to lack of funds or resources , oft - interrupted construction , and the British attack on Washington during the War of 1812 , work on the rotunda did not begin until 1818 .
Thornton had first conceived the idea of a central rotunda .