Clever groups and overlaps. Kind of fun to solve, but it was partly by lucky guesswork. Arguably all four of the Greco Roman entertainment venues group could swap with Colosseum, in the Landmarks of Rome group, so there could be five equally valid answers to the grid.The two groups are so close in subject matter, that it would be better to place Colosseum in the venues group and include another more modern landmark in the Landmarks group. It's a shame it doesn't work like a proper grid, as it was actually quite a nice, quick solve, and the other two links were clever.