Although this shares the circus setting as some others of the time, it's not primarily "about" the circus. It's a profound look at age, comeback, love (whether wanted or not), ambition. It's set in a dark and almost tawdry Paris of the mid-1950s, one that seems still tired and rather poor a dozen years after liberation.
The whole setting - and the love triangle - are fabulous yet realistic. This is a great bookend for An American in Paris - two entirely different images of Paris and France at the time.
The Burt Lancaster characterization is simply great - understated, powerful, moving - a man looking for a comeback, a last chance. Tony Curtis is also fine (I think Curtis has long been terribly underrated - he's a very good actor, wonderful in all kinds of parts from The Boston Strangler to Boeing, Boeing, from Sweet Smell of Success (with Lancaster again) to Some Like it Hot). Lollobrigida is great - a fine actress, yes unbelievably sexy but also just excellent at making us feel what her (desperate and cunning) character feels.
This is a great movie - amazingly set with a circus backdrop. I loved it. It's as good a depiction of post-war western Europe as can be imagined - in music, in light/shadow, in the fatigue you feel throughout. Watch it! You won't be disappointed.