What breed belongs big mountain dogs?

There is no breed called "Big Mountain Dog". It's possible that this is a made-up name or a nickname for a specific dog.

To help you figure out what breed you're looking for, please provide more details about the dog:

* What does it look like? (size, color, coat type, any unique features)

* Where did you see it? (online, in person, etc.)

* What other information do you know about it? (purpose, temperament, etc.)

Once you provide more details, I can help you identify the breed.