Afon Hafren

The longest flowing river in Britain. The Afon Hafren runs out of the sea of Môr Hafren, northward into Logres and into the Mynyddoedd Cymru, or Elenydd, Wales. 
Afon Hafren is its Welsh name, while it's also known as the Sæfern in Anglo-Saxon, or by its modern name: Severn. 
Latin: Sabrina