Human nature establishes it. Your rights derive from what is necessary to obey natural law; and since every individual has duties to himself, his family, and his community, he requires a body of property to discharge them.
But that right is not unlimited; you literally have no more right to private property than is necessary for you to satisfy your obligations under natural law. Thus, you have a right to be free from trespassing, but this right is not so unlimited that you could, for instance, licitly sue a person for trespassing who runs across your property to escape a murderer pursuing him.
I'll explain more later if you like, but for now, I'm off to bed.