The Roman Empire At Its Peak. By on May 30, 2013. Quantity is certainly not quality. Despite encompassing an incredible five million-plus square kilometers by 117 AD, that vast expanse surely wouldn’t be enjoyed for too much longer. As the empire expanded, the efficacy of its institutions contracted to the point that by 284 AD it was vulnerable to external attack and eventually collapsed. Savannah Cox is the Managing Editor of All That Is Interesting.