French police and troops are gearing up for their biggest security challenge since the deadly Nov. 13 attacks across Paris last year, as hundreds of thousands of fans mass in the French capital for Sunday's European Championship final.

Security forces have three key venues to protect when France plays Portugal: The Stade de France stadium hosting the final - outside of which three suicide bombers blew themselves up last year, the 92,000-capacity Fan Zone in the shadow of the Eiffel Tower, and the Champs-Elysees boulevard, which will likely be swamped with fans after the match.

Security forces have already successfully protected a total of 11 matches at the Stade de France and Paris stadium the Parc des Princes, including the tournament's opening match, but the final is expected to draw the biggest crowds as France aims to win its third European title by beating Cristiano Ronaldo's Portugal.

Troops have been patrolling the streets of Paris for months in the aftermath of two deadly attacks by Islamic extremists last year. As Portugal and France fans wandered along the Champs-Elysees on Saturday they passed army trucks and submachine gun-toting troops.

Meticulous security preparations began long before the tournament and included an exercise in March in which officials simulated an attack involving a chemical bomb at an open-air screening of a match, with thousands of spectators.

France has mobilized some 90,000 security agents around stadiums, fan zones and streets to bolster security. Interior Minister Bernard Cazeneuve has also kept his ministry's crisis room open throughout the tournament to help monitor events and coordinate responses should action be necessary.

The work has paid off so far.

On the eve of the final, tournament organizer UEFA paid tribute to the work of the French security forces in the 50 matches played in 10 host cities leading up to the final.

"We owe a great debt of thanks to the French people, to the French president, François Hollande, to the French government, the host cities, and the French police and armed forces, who have done such a marvelous job of ensuring the safety of the millions of fans who have come from all over Europe to attend this tournament," UEFA senior vice president Angel Maria Villar said Saturday.

Matches early in the June 10-July 10 tournament, most notably the 1-1 draw between England and Russia in Marseille, were marred by hooligan violence, but there have been no other major security problems at the a tournament.

"France has achieved something quite remarkable, delivering one of the world's biggest sporting events in very challenging circumstances," Villar said. "France has shown that adversity can be overcome. It has shown the world how to stand tall."