small round battle arena, 70 blocks...

small round battle arena, 70 blocks wide, empty flat floor of sand, surrounded by one solid smooth wall 8 blocks tall with no gaps, no stairs, no ledges, no blocks sticking out, wall made of prismarine, prismarine bricks, dark prismarine and sea lantern accents, decorations only on the outside of the wall: coral shapes, kelp, sea lantern pillars, water pools, no buildings, no roof, nothing inside the arena, minecraft 1.8 blocks only