Evidence of early habitation in Qatar that can be traced as far back as to the 4th century BC appeared in many artifacts such as inscriptions, rock carvings, flint spearheads and examples of pottery which were all uncovered by the Danish (1965), the British (1973) and the French (1976) expeditions. Researchers knew al-Wasil hills since 1957 as an important site of Stone Age archeology. About 200 archeological sites of the prehistoric age were discovered during the eight years of the work of the Danish expedition from 1965 to 1975. Several sites of various periods in the Stone Age were discovered to the east of Um Bab. Other sites were found in the southernmost border near Soudanthil. An important site for the manufacture of flint tools, which probably goes back to the Mesolithic Stone Age, was discovered at Umm Tag to the south west of Dukhan; and new sites were discovered to the south east of Mesaieed. The archeological surveys revealed that the Ubaid civilization, which flourished in southern Iraq and the northern parts of the Arabian Gulf, had also reached the Qatar peninsula. In the 5th century BC, the Greek historian Herodotus referred to the seafaring canaanites as the original inhabitants of Qatar. Further, the geographer Ptolemy showed in his map of the Arab world 'gatara' as believed to refer to the Qatari town of Zubarah, which has acquired the fame of being one of the most important trading ports in the gulf region at the time.