The Roman Empire was  about 4.4 million square kilometres in area for about 400 years, extending from north England, the  Rhine and the Danube to the edge of the Sahara and the first cataracts of the Nile, and from Portugal to the Caucasus and northern Iraq. That's about the same size as all South Asia.  Rome expanded to about 5 million sq km under Trajan, adding the Caucasus, Iraq, and the Carpathians, but couldn't hold them. The Chinese Tang was larger. However, Rome also completely encompassed the 2.5 million sq km of the Mediterranean, pacifying it for  trade and commerce and effectively turning it into a giant Roman lake. No medieval Indian empire completely encompassed the Indian subcontinent, whether the Guptas or Harsha or the Delhi Sultanate or the Mughals. The Delhi Sultanate under Mohammad ibn Tughluq in the early 14th century and the Mughals under Aurangzeb in the late 17th century came close  but couldn't manage to hold it even for a few years of those rulers' reigns.