When you type the name of an Emperor, 'nearby' Emperors will be revealed too. For example if an Emperor ruled for 5 years from 100 AD to 105 AD, any Emperor ruling within 5 years of that time span will also appear (so anyone ruling between 95 AD and 110 AD).
The names of Emperors can be typed either in English or in Italian.
Data from http://en.wikipedia.org/wiki/Emperors_of_Rome (hence Julius Caesar not included)
Not counting some minor sons who were made emperor under their father