Was the Persian Empire bigger than the Roman Empire?

here are the two empires at their height:

Persian: http://www.cais-soas.com/CAIS/Images2/Maps/Achaemenid_Empire_Map.bmp

Roman: http://www.dkimages.com/discover/previews796379533.JPG

The Persian Empire is greatest in area. Whether it was bigger depends on what criteria you want to measure the two against - population, wealth etc.