Tāq Kasrā (Arabic: طاق كسرى‎, romanized: ṭāq kisrā, also transcribed as Taq-i Kisra or Taq-e Kesra (Persian: طاق کسری‎) or Ayvān-e Kesrā (Persian: ایوان خسرو‎, romanized: ʼiwan-i-husraw, meaning Iwan of Chosroes) are the remains of a Sasanian-era Persian monument, dated to c. the 3rd to 6th-century, which is sometimes called the Arch of Ctesiphon. It is located near the modern town of Salman Pak, Iraq. It is the only visible remaining structure of the ancient city of Ctesiphon. The archway is considered a landmark in the history of architecture, and is the largest single-span vault of unreinforced brickwork in the world.