In what way was Roman law a civil law system?

During the period of the republic (753–31 BCE), the jus civile (civil law) developed. Based on custom or legislation, it applied exclusively to Roman citizens. … Roman law, like other ancient systems, originally adopted the principle of personality—that is, that the law of the state applied only to its citizens.

the first forms of writing came from them in the form of pictographs around 3100 bc.