What a guardian dog was made to do
The Great Pyrenees comes from the Pyrenees Mountains between France and Spain. Shepherds there kept large white dogs to live with their flocks and guard them from wolves and bears. The dogs worked with little human direction. They were chosen for calm, steady, and independent guarding. The breed also became fashionable at the French court, and one often-told story says Louis XIV named it the Royal Dog of France. Today they still guard livestock, and many live as family dogs.
Pyrs stayed with the flock day and night and made decisions alone. That helps explain why many bark at night, patrol the boundaries, and are slow to respond to cues. See our Great Pyrenees guide for more.
It is worth saying that each dog is different. Some Pyrs are mellow and quiet, and some are chatty. But if you live with a Pyr who barks and roams, you are living with the breed doing its job.