The remains of one of the most important Neolithic Greek and European settlements sits on the Kastraki hill, near the modern village of Sesklo. The site, which gives its name to a Neolithic culture found throughout Thessaly, was inhabited from the Early Neolithic period (seventh millennium BC) until the Middle Bronze Age, though it flourished mostly in the Middle Neolithic period (fifth millennium BC). Judging by the longevity of the prehistoric settlement, the choice of the site was auspicious. Indeed, it has all the features coveted by early settlers: deep seasonal streams with ample water supply, flatlands for cultivation, hills and the sea nearby.

The first settlers arrived at Sesklo in the middle of the seventh millennium BC, during the Pre-ceramic Neolithic. Sesklo is one of the most important sites for our knowledge of this period in Greece, since it demonstrates clearly the so-called 'Neolithic triptych' of sedentary habitation, agriculture and animal husbandry. The size of this first settlement (Sesklo A) is impossible to determine because of later occupation. However, traces of this period located 125 metres beyond the hill's northeast border (Sesklo C) show that it was quite large. Shallow circular depressions, the narrow foundation trenches of a rectangular building and pieces of clay used as building material are all that remains of the settlement's makeshift houses. The settlement contained very few objects, such as obsidian and chert blades, stone and bone tools and terracotta figurines. Its inhabitants lived off agriculture and animal husbandry.

Traces of the larger, Early Neolithic, settlement of the sixth millennium BC were identified on the hill (Sesklo A), but also on the plain to the west (Sesklo B) and in the surrounding area. The main characteristic of this period is the variety of building types and building materials. Some buildings were made with stone foundations and brick walls, others were made of wood and clay, and some were outlined with standing stone slabs. The inhabitants of this settlement used simple stone and bone tools, terracotta figurines and terracotta vases - both monochrome and with painted decoration.

Sesklo was at its peak during the Middle Neolithic when it occupied an area of approximately 100,000 square metres, which included the Kastraki Hill (Sesklo A), the plain (Sesklo B) and the surrounding area. On the hill, the settlement's 500-800 dwellings were densely arranged, with narrow streets and squares running between them, surrounded by large retaining walls. The dwellings in the plain were larger and more separated. All houses had stone foundations, mud brick walls, timber two-sloped roofs and chimneys. The pottery of this period, also known as the 'Sesklo culture', is used to date the different phases of the Middle Neolithic period. Vases are handmade, usually with painted decoration. Improved firing techniques account for the beautiful red colour of the motifs painted on a white background. The settlement's inhabitants used a larger number and variety of stone tools than before, including tools made of obsidian imported from the island of Melos. The settlement burned down towards the end of the fifth millennium BC and only the hilltop was re-inhabited 500 years later, in the Late Neolithic. A 'megaron' was built during this later period at the highest point of the hill, in the middle of the new settlement, surrounded by a system of circular stone enclosures. The settlement lived on throughout the Early and Middle Bronze Ages. Several houses at Sesklo A and the cist graves uncovered at Sesklo A and B belong to this period.

The settlement was discovered in the late nineteenth century and Christos Tsountas was the first to excavate on Kastraki hill in 1901-1902. Dimitris Theocharis began new excavations on the hilltop in 1956 and investigated the surrounding area in 1972, revealing the large Middle Neolithic settlement. The site continues to be weeded.