The archaeological site of Halos lies on either side of the national Athens-Thessaloniki highway. It consists of the Lower town, which occupies the plain, and the Upper town, which climbs the eastern slopes of a low rocky crag, the so-called Kastro. The Upper town was surrounded by walls running down the hillside in a V-shape from the summit to the corners of the Lower town defences. The peak of the Upper town triangle was occupied by a small triangular acropolis, which was accessed through a gate at the centre of the northern wall. A possible temple was excavated in the southeast sector of the Upper town, where most of the city's public buildings appear to have been located. The acropolis was later crowned by a Byzantine fortress (twelfth century AD) with elongated shape and many towers.

A wall approximately 4.5 kilometres long, with 117 defence towers, surrounded the Lower town forming a rectangle. The wall, which is visible on either side of the national road, is generally preserved to a height of three courses of limestone blocks except near the southeast gate were four to seven courses are preserved. Traces of the wall's upper, brick corses are still visible in places, while the maximum preserved height of the wall is 2.5 metres. The town was accessed through two main gates to the northwest and southeast, and possibly several smaller ones. Two large avenues lead from these two gates into the town and together with other streets divided the town into a regular grid of quarters and town blocks. The streets and houses have practically disappeared, but we can estimate that the Lower town had approximately 1400 houses and workshops, where 8,000-9,000 people lived. So far, six houses, several roads, workshops and kilns used in the production of terracotta vases and objects have been excavated. The simple but spacious houses had three to five rooms, storerooms and an internal courtyard. Their walls were of brick with stone foundations and the roofs had terracotta tiles. Outside the town lie the cemeteries revealed during recent excavations.