Answer
Al-Idrisi, a 12th-century Arab geographer, underestimated the size of Europe. His map of the world, known as the Tabula Rogeriana, depicted Europe as much smaller than it actually is. This error likely stemmed from a lack of accurate information about the continent at the time. Despite this mistake, al-Idrisi's map was a significant contribution to medieval cartography and provided valuable insights into the geographical knowledge of the period.