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I don't have sufficient context to write an accurate overview of "257." The context provided only indicates "year," but I need more information about what "257" refers to—whether it's a historical year, a scientific measurement, an event, a publication, or something else—to give you an accurate and meaningful overview. Could you provide additional context about what "257" is?
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Article
Golden Roman helmet found near Sirmium (Serbia)
Year 257 (CCLVII) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Valerianus and Gallienus (or, less frequently, year 1010 Ab urbe condita). The denomination 257 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.