Portugal is getting ready for a NATO summit at the end of the week, at which leaders are expected to outline plans for a progressive withdrawal of troops from Afghanistan.
The two-day meeting in Lisbon will also look to redefine the strategy of the western military alliance in the face of threats from terrorists, cyberattacks and rogue states.
Portugal has temporarily suspended Schengen agreement rules, and is imposing border controls.
Some local people are somewhat bemused by the security. One man on the Portuguese-Spanish border said it was not the first time he had been stopped, and he did not know why.
Lisbon’s security chief has said exercises being carried during the last few days before the summit should help detect any problems.
A strong military presence will include the Portuguese navy and air force. The summit is expected to bring more than five thousand people to the capital.