It was one of a number of heightened security measures in place for Sunday's Flight of the Angel show - one of the highlights of the two-week carnival.
Police checked bags and used metal-detecting wands before allowing carnival-goers into St Mark's Square.
Those allowed in saw a beauty pageant winner ride a zipwire over the crowd into the square.
Wearing beautiful hand-painted masks and elaborate costumes to stroll around the canals of Venice is a key part of the carnival, which is believed to have started in the 11th Century after a military victory.
The authorities decided to increase surveillance during the festival following November's attacks in Paris, but rejected a plan to ban people from wearing masks.
Venice police chief Angelo Sanna told The Associated Press when the event got under way a week ago that the discussion about masks was approached "with balance and attention, because carnival is the masks. It is difficult to have carnival without them."
He said spot checks of masked-revellers would be made to verify identities, and more officers - both in uniform and under-cover - would be posted around the city during the length of the event.
The carnival will end on 9 February, marking the start of the Christian observance of Lent.
Revellers at the annual carnival in Venice were briefly asked to lift their masks before going in to the event.