By modern New Testament Scholars the Gospel according to Mark is considered as the oldest of the existing gospels. It is dated to around 70 AD, because of the nature of its reference to the destruction of Jerusalem in chapter 13. In Mark we hear that Jesus says that the temple of Jerusalem will soon be destructed. This is our most important way of dating Mark. Beyond this, the dating is not founded in any traditional historical sources, but is reconstructed on the base of secondary sources.
Early tradition claims that the gospel was written in Rome.
This is connected to the notion where John Mark wrote down from the narration of disciple Peter. But this is highly doubtful as the John Mark was a Jew, and there are clear indications in the text that the author of the gospel was not Jewish. A more accepted theory is that the gospel was written by a member or a group of members in a community that associated themselves with Mark, or that was founded by Mark, or even written by an unknown Christian named Mark. Modern scholars suggest Galilee or Syria as likely places of origin. If the traditional view of the gospel's origin is to be discarded, most scholars suggest that the the author of Mark used were not only oral, but also in form of text documents.