AI overview
I don't have enough context to write an accurate overview of "639." The single word "year" doesn't clarify what "639" refers to—whether it's a year in history, a code, a reference number, or something else entirely. Could you provide more information about what "639" is?
AI-generated from the Wikipedia summary — may contain errors.
Article
The Muslim invasion of Egypt (639–642)
Year 639 (DCXXXIX) was a common year starting on Friday of the Julian calendar. The denomination 639 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.