An Elite Guard Dalek, under orders from the Dalek Emperor, led a group of Silver Daleks in a time machine to Earth, 37 AD, to assert Dalek control over Emperor Caligula during the time of the Roman Empire.
The Elite Guard declared that Caligula's violent and aggressive tendencies made him ideal for subjugation; with him under Dalek control, he would make an excellent puppet through which the Daleks could rule the empire for themselves and take command of Earth's history.
However, Caligula had an adverse reaction to his conditioning. He was driven to display numerous insane behaviours and ultimately resisted his conditioning when the Elite Guard tried to reassert it.
Concluding that the human mind was too primitive for Dalek control to hold in this time period, the Elite Guard abandoned the mission and returned to Skaro, but it intended to run the experiment again at a different nexus point in human history. (COMIC: Empire of the Daleks)