To understand the Pyrenean mountain dog, one must be aware what the purpose of the dog is. His physique equals the body of the shepherd, to what the sheep herd expects in the mountains.
His traits were for the same purpose applied.
His presence
The mountain dog is a watch dog who let his presence known by barking with his loud voice.
During his defense tasks the Pyrenean mountain dog must let his presence quickly know to intruders. He lets this know by his very loud voice.
Since centuries you can hear the dogs loud voice reflect by dawn in the valley. They do this by letting their presence known to each other.
What they can do in the in the mountains they can't do in the city, that's why you must avoid letting them outside before dawn. Knowing that the Pyrenean mountain dog is loud by nature it's important when choosing this race. Take this in consideration, if you don't want to abandon the dog due his loud bark.
Responsibility
While completing his tasks he will not let man or animal approach his territory. If he feels a threat he is capable of attacking, so the dog protects what is threatened.
As companion he is an excellent watchdog. He is suspicious to persons he doesn't know and very careful in unusual situations.
To this day his protective instinct has become very territorial since he protects a territory that's very well marked. He even protects more then you might expect. He thinks his territory bigger then the boarders of your house.
As result that he will have trouble of letting other dogs pass by your porch.