 <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 ). <yor> Apakan pataki fun idahun ibeere yii ni: Ijọba naa de ibi ti o tobi julọ labẹ Trajan (ọba 98 - 117), ti o ni agbegbe ti 5 milionu square kilomita. Ìdáhùn náà ni pé, lábẹ́ ìjọba Trajan (tó ṣàkóso láti ọdún 98 sí 117 Sànmánì Kristẹni). 