We select a particular coin for each year. Coins tell us much about history, and indeed provide a historical record. Certain coins are strongly associated with a particular date, even though there may be other dates of the same coin. Mention 1780 to most coin dealers, and they will instantly call the silver Maria Theresa thaler to mind, simply because it has been restruck (re-issued) with the same "frozen" date as a commemorative coin ever since her death.