There are 2 Arcadias:
- The city of Arcadia, which was Gallifrey's "second city" (according to the Eleventh Doctor, in "The Day of the Doctor"). The Fall of Arcadia (to the Daleks) was mentioned with great bitterness by the Tenth Doctor in "Doomsday" & featured in "The Last Day".
- The planet Arcadia, mentioned by Amy Pond at the start of "Vincent and the Doctor" as somewhere the Eleventh Doctor had taken her. (We were not shown their visit to that planet.)