For others, the term Dark Ages is intended to be neutral, expressing the idea that the events of the period seem 'dark' to us because of the paucity of the historical record. The term is used in this sense (often in the singular) to reference the Bronze Age collapse and the subsequent Greek Dark Ages, the brief Parthian Dark Age (1st century BC), the dark ages of Cambodia (c. 1450–1863 AD), and also a hypothetical Digital Dark Age which would ensue if the electronic documents produced in the current period were to become unreadable at some point in the future. Some Byzantinists have used the term "Byzantine Dark Ages" to refer to the period from the earliest Muslim conquests to about 800, because there are no extant historical texts in Greek from this period, and thus the history of the Byzantine Empire and its territories that were conquered by the Muslims is poorly understood and must be reconstructed from other contemporaneous sources, such as religious texts. The term "dark age" is not restricted to the discipline of history. Since the archaeological evidence for some periods is abundant and for others scanty, there are also archaeological dark ages. Since the Late Middle Ages significantly overlap with the Renaissance, the term 'Dark Ages' has become restricted to distinct times and places in medieval Europe. Thus the 5th and 6th centuries in Britain, at the height of the Saxon invasions, have been called "the darkest of the Dark Ages", in view of the societal collapse of the period and the consequent lack of historical records. Further south and east, the same was true in the formerly Roman province of Dacia, where history after the Roman withdrawal went unrecorded for centuries as Slavs, Avars, Bulgars, and others struggled for supremacy in the Danube basin, and events there are still disputed. However, at this time the Abbasid Caliphate is often considered to have experienced its Golden Age rather than Dark Age; consequently, usage of the term must also specify a geography. While Petrarch's concept of a Dark Age corresponded to a mostly Christian period following pre-Christian Rome, today the term mainly applies to the cultures and periods in Europe that were least Christianized, and thus most sparsely covered by chronicles and other contemporary sources, at the time mostly written by Catholic clergy. However, from the later 20th century onward, other historians became critical even of this nonjudgmental use of the term, for two main reasons. Firstly, it is questionable whether it is ever possible to use the term in a neutral way: scholars may intend this, but ordinary readers may not understand it so.