Where did the phrase "draw a line in the sand" come from?

According to Wikipedia:

When the guardians of King Ptolemy VI of Egypt demanded the return of Coele-Syria in 170 BC, Antiochus launched a preemptive strike against Egypt, conquering all but Alexandriaand capturing King Ptolemy. To avoid alarming Rome, Antiochus allowed Ptolemy VI to continue ruling as a Puppet-king. Upon Antiochus' withdrawal, the city of Alexandria chose a new King, one of Ptolemy's brothers, also named Ptolemy (VIII Euergetes). Instead of fighting a civil war, the Ptolemy brothers agreed to rule Egypt jointly.

In 168 BC Antiochus led a second attack on Egypt and also sent a fleet to capture Cyprus. Before reaching Alexandria, his path was blocked by a single, old Roman ambassador named Gaius Popillius Laenas, who delivered a message from the Roman Senate directing Antiochus to withdraw his armies from Egypt and Cyprus, or consider themselves in a state of war with the Roman Republic. Antiochus said he would discuss it with his council, whereupon the Roman envoy drew a line in the sand around him and said, "Before you cross this circle I want you to give me a reply for the Roman Senate" - implying that Rome would declare war if the King stepped out of the circle without committing to leave Egypt immediately. Weighing his options, Antiochus wisely decided to withdraw. Only then did Popillius agree to shake hands with him.^[5]