The Hellenistic city of Halos lies on a narrow strip of land in the eastern part of the Almyros plain, between Mount Othrys and the Pagasitikos Gulf. Its location was strategic in antiquity, since it controlled the road connecting southern and northern Greece. Its creation in the late fourth century BC is due to the military campaigns of the Macedonian kings Demetrios Poliorketes and Cassander in Magnesia.

According to mythology, the city was founded by the legendary King Athamantas, whose children, Phrixos and Helle, are depicted on the city's bronze coins riding the golden ram on their journey to the Black Sea. Recent rescue excavations show that the area was continuously occupied from the Late Bronze Age to the Iron Age, and in the Archaic and Hellenistic periods. The city's long history is mostly illustrated by its cemeteries and to a lesser extent by its architectural remains. Scant remains of a ninth-eighth century BC township were identified within the limits of Hellenistic Halos. These include parts of apsidal buildings with storerooms, adjacent rubbish pits and intramural children's burials. The cemeteries of the ninth century BC are large, with numerous graves displaying various funerary practices (burials and cremations). The archaeological finds prove the township's importance and development during subsequent centuries, although its name remains unknown. Could it be Homer's Halos?

The Hellenistic town was founded c. 302 BC and destroyed approximately thirty-five years later, c. 265 BC, probably by an earthquake. It was not entirely abandoned, however, as squatters continued to occupy makeshift houses and buildings near the city gates until the second century BC. Bronze and silver coins dating from the mid-fourth to the second century BC, show that Halos had contacts with cities in Thessaly, Euboia, Phtiotis and Macedonia. Excavation finds indicate that its inhabitants were involved in agriculture, animal husbandry and fishing, and, to a lesser extent in hunting.

Remnant of the defences and dwellings stood on the plain and the nearby hill for many centuries, and were described by several travellers. However, intensive farming and quarrying of ancient building material eventually destroyed what remained. Systematic archaeological research in the area began in the 1970's and continues to this day under the Thirteenth Ephorate of Prehistoric and Classical Antiquities and the Dutch Archaeological Institute. In 1976 to1990, research focused on the town's topographical layout (fortifications, grid plan) and the investigation of a number of houses, while in 1990-2003 excavations revealed the town's southeast central gate, which remained in use after the destruction of the city in the mid-third century BC, and cemeteries located outside the city walls. A study for the presentation of the monuments of Halos and the construction of facilities for visitors was recently completed.