Many of these are astronomical events. Calendars are usually simple methods for dividing up years. Often based on moon phases, solstices. Astronomical observatories were fairly common. Most of our reckoning of dates follows some system like them.
Some chronological markers provide a link to the calendar.
For example, since each Roman emperor had his own face stamped on coins during his realm, and dates for emporer's realms are known from historical records, the date a coin was minted may be discerned by identifying the emperor depicted . But there are certainly drawbacks. Outside of the context of a single site or society, a coin's date is useless. Even within that context, it is a minimum date , that is, the site can be no earlier that the date of the coin or object. And, outside of certain periods in our past, there simply were no chronologically dated objects, or the necessary depth and detail of history that would assist in chronologically dating civilizations.