Phthiotis covers the northern and southern shorelines of theMalian Gulf, an inlet of theAegean Sea. It stretches inland towards the west along the valley of the riverSpercheios. In the south it covers the upper part of theCephissus valley. There are several mountain ranges in Phthiotis, including theOthrys in the northeast, theTymfristos in the west, theVardousia in the southwest,Oeta in the south and theKallidromo in the southeast.
"Phthiotis" means "the region ofPhthia", the southernmost region of ancientThessaly aroundPharsalus and home ofAchilles. InClassical times, it also referred to the region ofAchaea Phthiotis, which bordered on Thessalian Phthiotis to the south and east. Achaea Phthiotis covered the northern part of the present regional unit Phthiotis and the southern part of presentMagnesia. The southeastern part of present Phthiotis was covered by the ancient regionLocris, and the southwestern part was ancientMalis andAinis.
The prefecturePhthiotis and Phocis was created in 1845. In 1947 this prefecture was split into the southern partPhocis and the northern part Phthiotis. As a part of the 2011 Kallikratis government reform, the regional unit Phthiotis was created out of the former prefecture Phthiotis (Greek:Νομός Φθιώτιδας). The prefecture had the same territory as the present regional unit. At the same time, the municipalities were reorganised, according to the table below.[2]