Doug and Tony are lying unconscious inside the crypt, when Nero's ghost nears them; the music playing in the background was taken from The Day the Earth Stood Still (1951), in particular from the "Klaatu barada nikto" scene.
This episode takes place in the Italian Alps in Villa Galba, Northern Italy on October 23, 1915 and in Arizona in 1968.
Whit Bissell (General Kirk) and John Hoyt (Dr. Steinholtz) appeared together in Brute Force (1947) nearly 20 years earlier.