Kind of general knowledge

1234567
Across
  1. 4. a place where gladiators fight
  2. 5. A roman soldier armed with a sword and shield
  3. 7. A near indestructible material
Down
  1. 1. A material like oobleck and jelly
  2. 2. A train driven by smoke and gears
  3. 3. A class of gladiators with a trident and a net
  4. 6. A common reading/writing/spelling subject