ATHENS, Greece -- The $1.5 billion security measures are in place. But where is the enemy?

The largest peacetime security operation involving a sporting event has turned Greece into a country poised to counter a full-blown military invasion.

More than 70,000 law enforcement personnel and troops are deployed at Olympic sites. Another 35,000 troops are guarding railways and borders, while Greece's entire armed forces of more than 150,000 active duty personnel are on high alert.

There are 50 warships and more than 200 planes, including fighters monitoring a no-fly zone over Athens. Also deployed are 120 U.S.-made Patriot missiles, Russian S-300 missile batteries and Greece's entire air defense network.

"Welcome to fortress Greece," read the headline of the daily Eleftherotypia, as thousands of visitors poured into the Greek capital for the Olympic Games on Friday.

The 255 million euro ($312 million) Olympic security system features an electronic web of more than 1,000 high-resolution and infrared cameras, 12 patrol boats, 4,000 vehicles, nine helicopters, a sensor-laden blimp, and four mobile command centers, all of which gather images and audio and relay them to a command center.

At sea, NATO's entire Mediterranean fleet is patrolling alongside Israeli and American warships. On the ground, some 200 NATO troops from its chemical and biological battalion are camped at a Greek army base. A rapid reaction unit, mainly of U.S. special forces, is on standby in Germany.

One of the smallest countries to host the Summer Games, Greece is spending an unprecedented 1.2 billion euro ($1.5 billion) for security, or about 20 percent of its 2003 defense budget.

Some Athenians question the outrageous price tag.

"I believe that if a terrorist wants to strike, they will. It's all about perception; in reality, we can do nothing," said Artenis Strouza, 45, a vendor selling Olympics pins. "All we can do is thank those who have asked us to pay so much for all this," he added, with sarcasm.

Greece is holding the first Summer Olympics since the Sept. 11, 2001, terrorist attacks against the United States. It has been under tremendous pressure to prepare for the worst-case scenario -- even if the enemy never shows up.

"The pressure, the stress and the agony in view of the great responsibility that we had to develop the Olympic security planning ... was enormous," Greek police spokesman Col. Lefteris Ikonomou told The Associated Press.

The security concerns have eased somewhat since Friday night, when the opening ceremony went off without a hitch.

"The opening ceremony was a determining moment in terms of security, given that we had the presence of several heads of state and the first massive movement of athletes to the Olympic stadium," Ikonomou said.

Some argue that even if there is no terrorist attack, it won't necessarily mean the security measures were successful.

Boaz Ganor, director of the International Policy Institute for Counterterrorism in Israel, said terrorists may have simply decided that an attack in Athens would not serve their interests or political message.

"Although Greek authorities invested a huge sum of money in the security measures, in my view, it is far from reaching maximum security, or even close to that," Ganor said, citing the need for enormous foreign assistance.

Athens revised its security budget upward several times amid increasing international concerns surrounding the safety of the Olympics after terrorist attacks in the United States, Turkey, and Spain.

The high cost of security is expected to be at the center of an international debate after the games.

"If the Olympic Games (are not) attacked, we probably are going to witness a lot of criticism for the huge expenses for security," Ganor said.

Ikonomou argued Greece was obligated to fulfill its responsibility.

"The international security environment dictates having a plan that is complete," he said.

Mike Rose, 53, an American tourist in town for the games, said he was impressed by the security setup.

"It's visible, but not oppressive or restrictive," Rose said.

But worth the cost?

"Only time will tell," he said.