In a number of different situations, the Torah requires that payment be made. What coinage had to be used to fulfill those requirements?
The Mishna teaches that:
The five sela of a firstborn must be made in maneh Tzori (silver Tyrian coin).
The thirty shekels of a slave (Shemot 21:32) and likewise the fifty shekels paid by a rapist (Devarim 22:29) and by a seducer (Shemot 22:16) and the one hundred shekels paid by the defamer (Devarim 22:19), in all these cases the holy shekel is meant, paid in maneh Tzori.
Generally speaking, during the time of the Talmud there were two types of coins. Matbe’ah Tzori was a silver-based coin that was viewed as being biblical money. Kesef medina were coins that had the same names as the more valuable matbe’ah Tzori, but were made of cheaper metals and were worth one-eighth the value of kesef Tzori. These coins were used for payments whose obligations were of Rabbinic origin. Different values for coins with identical names were not uncommon in the ancient world and this phenomenon still exists in some places today, where paper money may have the same name as a gold coin, for example, but is worth significantly less. It is therefore essential to determine which coin is being discussed.
According to the Gemara, all of the payments listed in our Mishna had to be made using the value of a holy shekel. The Melekhet Shlomo suggests that the Mishna separates the case of the firstborn from the other cases because it does not want to mix the case of a mitzva with the cases of payment for violent or anti-social acts. He also quotes the Ritva as teaching that there is a distinction between the cases. Whereas the payment of five shekalim for redeeming the firstborn remains at the original value even in the event of currency fluctuation, the other cases will depend on the value of the coin at a given time.