The term 'Historical Spans' refers to the length of time that a particular event or period of history has lasted. The crossword solution for this term is 'ERAS', which can be defined as a period of time marked by a distinctive character or a set of events. ERAS are typically divided into smaller periods of time, such as centuries or decades, and can span hundreds or even thousands of years. Historical Spans are often used to measure the progress of civilizations, cultures, and societies over time.