The ancient term "Hellas" was already in use in the 6th century to designate southern Greece in an administrative context, being employed in the Synekdemos as an alternative name for the Roman province of Achaea.

[1][2] During the late 6th and early 7th centuries, the collapse of the Byzantine Empire's Danube frontier allowed large-scale Slavic invasions and settlements to occur all over the Balkan peninsula.

Aided by the Byzantine Empire's preoccupation with the long and bloody wars with Sassanid Persia in the east, and with the Avar Khaganate in the north, the Slavs raided and settled almost at will.

The Slavic settlement that followed the raids in the late 6th and early 7th centuries affected the Peloponnese in the south and Macedonia in the north far more than Thessaly or Central Greece, with the fortified towns largely remaining in the hands of the native Greek population.

[5] It was not until the reign of Leo III the Isaurian (r. 717–741) that major land operations are recorded, and not until the early 9th century that the re-establishment of imperial control in the hinterland was completed.

In Central Greece and Thessaly, the campaign seems to have been mostly a show of force to strengthen imperial rule and subdue the new settlers, while in the Peloponnese it probably involved actual fighting against the Slavs.

[20] During the 10th and 11th centuries, Hellas was often governed jointly with the Peloponnese under a single strategos, and as the civilian administration rose in importance, the same practice appears there as well, with protonotarioi, praetores and kritai being appointed for both themes.

[1][21][22] Thessaly appears to have been detached from Hellas and joined to the theme of Thessalonica from the early 11th century—though the Spercheios valley remained part of Hellas—until sometime in the 12th century.

[20] The Italian maritime republics, with the Republic of Venice first and foremost, began to establish their presence in the region towards the end of the century, signalling the beginning of the Italians' ascendancy in maritime commerce and their gradual takeover of the Byzantine economy: in the aftermath of the failed Norman invasion, Alexios I granted the first trading privileges to the Venetians in exchange for their naval aids against Norman fleets, such as immunity from taxation and the right to set up trade colonies in certain towns including Constantinople itself.

Coupled with the corruption and autocratic behaviour of officials, this led to a decline in industry and the impoverishment of the peasantry, eloquently lamented by the Metropolitan of Athens, Michael Choniates.

Having become the master of a quasi-independent realm encompassing much of southern Greece he then tried to legitimize his position by marrying the daughter of the deposed Alexios III Angelos at Larissa.

[31] Boniface divided the captured lands among his followers; the main Latin states formed in the former area of Hellas were the Duchy of Athens, the Marquisate of Bodonitsa, parts of the Kingdom of Thessalonica, the Lordship of Salona, and the Triarchy of Negroponte.