I've been dabbling in 54mm Gladiators for a long time, almost two years. I really like the scale of 54mm-- it's easy to paint and easy to play with. For as long as I've been involved in this scale, I've enjoyed the spectacle of big figures, but there's never really been a decent solution for a coliseum.
Sure, I could have gone with the Ben Hur Coliseum playset. You can still get this in recast plastic-- but it doesn't look like a Coliseum to me, and it costs an arm and a leg to find one in any decent shape.
The figures are kind of playmobil like, but I gave them to Gar (with the chariot), keeping the shields and weapons for gladiator games as missing weapon tokens. The coliseum itself is made of a semi-soft plastic (not rigid), with lots of fine detailing in the statuary and tiling and mosaics. The scale is just perfect for 54mm. At this moment, I have primed it with Kryolan Fusion plastic paint, and I'm tempted to leave it be, or give it another coat-- the kryolan gives it a sort of marble finish. I'll have to paint the door and fixture details, of course, to give it some contrasts. I am pleased with the investment, which was fairly minimal compared to picking up an entire Ben Hur playset, and frankly I think this looks better.