What is the theme?

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Across
  1. 3. A British television show which portrays life at a typical comprehensive school (6,4)
  2. 4. Land alongside the edge of a river
  3. 6. A vibrant market in North Yorkshire
  4. 8. A fortified structure built in the middle ages
  5. 9. A type of structure created explicitly to commemorate a person or event
  6. 10. An animal that never forgets
Down
  1. 1. Football player that began his career at Crystal Palace. First name Gareth.
  2. 2. Famous bear that likes to eat marmalade sandwiches
  3. 5. Character from Buffy the Vampire Slayer played by David Boreanaz
  4. 7. Shape resembling that of an egg