Catabathmus was the name of a large promontory, which was considered the frontier between Ptolemaic and Roman Egypt and Cyrenaica. The road along the coast is inaccessible, but there is an inland road, the Halfaya Pass, which is about 180 meters above the level of the nearby sea. The slope is mentioned by Polybius, Pomponius Mela, Pliny the Elder, and Orosius.note[Polybius, World History 31.18.9; Pomponius Mela, Choreographia 1.41; Pliny the Elder, Natural History 5.38; Orosius, History against the Pagans 1.2.88.] Going up and down is not very easy, making Catabathmus, "the descent", an important obstacle and a logical border. When Ptolemy VIII Physcon had to reconquer the Cyrenaica (162 BCE), he met resistance at this place.note[Polybius, World History 31.18.9.]
The Graeco-Roman geographer Strabo mentions it as the most western point of Egypt,note[Strabo, Geography 17.1.5.] as the most eastern point of Cyrenaica,note[Strabo, Geography 17.3.22.] and also knows that the area was destitute of water.note[Strabo, Geography 17.3.1; cf. Solinus, 27.3.] The site was fortified and called Tetrapyrgia, "four towers", while its harbor was called Plynus.note[Strabo, Geography 17.3.22; cf. Polybius, World History 31.18.11.] Several other ancient authors mention the town: the Roman author Sallust knows that it is along the coastal road, while the Alexandrian scientist Ptolemy offers coordinates.note[Sallust, War against Jugurtha 19.3; Ptolemy, Geography 4.5.]
Today, the town is known as Sallum or Sollum; in the Second World War, the Halfaya Pass became notorious as the Hellfire Pass.