If ancient aliens visited Earth, can evidence of their existence be found in the mysterious structures that still stand throughout the world?

Andrew Collins, Christopher Dunn, David Childress, David Wilcock, Erich von Däniken, George Noory, Giorgio A. Tsoukalos, Graham Hancock, Jason Martell, John Brandenburg, Jorge Luis Delgado Mamani, Linda Moulton Howe, Nicholas Howarth, Philip Coppens, Robert Schoch, Rusty McClure, Sara Seager