 
 <translate> 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 ). <hau> Muhimmin bangare don amsa wannan tambayar shine: Daular ta kai mafi girman girmanta a ƙarƙashin Trajan (mulkin 98 - 117), wanda ya ƙunshi yanki na murabba'in kilomita miliyan 5. Amsar ita ce: a ƙarƙashin Trajan (ya yi sarauta daga shekara ta 98 zuwa 117). 