 
<translate> Akụkụ dị mkpa maka ịza ajụjụ a bụ: Alaeze Ukwu ahụ ruru ebe kachasị ukwuu n'okpuru Trajan (chịrị 98 - 117), na-ekpuchi mpaghara nke 5 nde square kilomita. Azịza ya bụ: n'oge ọchịchị Trajan (ọ chịrị malite n'afọ 98 ruo 117 O.A.). <eng> The important part for answering this question is: The Empire reached its largest expanse under Trajan (reigned 98 -- 117), encompassing an area of 5 million square kilometres.
The answer: under Trajan ( reigned 98 -- 117 ). 