The remains of ancient Pharsalus lie on the northern slope of a hill of the Narthakion mountain and occupy almost the same area as the modern town. Although the ancient circuit is preserved mainly on the southern part of the hillside, its total length is estimated as no more than 5 kms. During the Byzantine era the ancient acropolis was reused but the town itself was restricted considerably to a small area just below it. The acropolis was of equal importance in the post Byzantine period as repairs of the previous walls or construction of new ones bear witness to.

A series of eleven small towers one close to the other protected the easily accesible southwestern flank of the city. Besides, seven other towers dispersed over several parts of the circuit are visible as well as four gates and two posterns. Two of the gates opened onto the acropolis walls.

At least four succesive periods of construction of the ancient walls have been identified, as can be concluded by the study of the preserved parts of the walls and the results of archaeological excavations. First in the series is that part of the walls built to a manner akin to the dry and rubble system with large and irregular blocks . This method of building serves as evidence dating the walls back to to the 6th century BC. The greatest part of the circuit is consistently built as an isodomic trapezoidal with quarry or hammer face and dates well back into the first decades of the 4th century BC. The headers and stretches system dates to not long after, probably in the middle of the same century. The city flourished in the second half of the 4th century BC under the support offered by its alliance with the Macedonian kings.