According to the Mishna, when a man marries a woman by means of money, the minimum amount is, according to Beit Hillel, a peruta or, according to Beit Shammai, a dinar. While Beit Hillel‘s position is fairly easy to understand, Beit Shammai‘s position demands some explanation, and it is discussed on our daf.
Rabbi Zeira suggests that Beit Shammai is simply looking out for the honor of Jewish women, who demand more than a small denomination coin. Rav Yosef suggests that the need for a dinar is based on the teaching of Rav Yehuda quoting Rav Asi, who rules that money required by the Torah is kesef tzuri while money required by the rabbinic sages is kesef medinah.
Generally speaking, during the time of the Talmud there were two types of coins. Matbe’ah tzuri was a silver-based coin that was viewed as being biblical money. Kesef medinah were coins that had the same names as the more valuable matbe’ah tzuri, but were made of cheaper metals and were worth one-eighth the value of kesef tzuri. 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 Beit Shammai, since we are dealing with a biblical law, we look for the smallest coin that was used in kesef tzuri, which was the equivalent of a dinar.
The dinar discussed in the Mishna was a silver coin, popular in the Roman Empire. It weighed about 3.9 grams, although in later times the pure silver was mixed with copper and it became devalued. Popular figures on a Roman dinar were Nero and Vespasian.