Jerusalem's Tyrian Shekel
In the second century BCE, Rome, the ruling power, operated two mints in the Mediteranean region, one in Lebanon at Tyre, and the second at Antioch. The mint in Tyre produced Tyrian Shekels and Half-Shekels, of a 95% silver purity, between the years 127 BCE and 19 BCE. In the year 19 BCE Rome closed the mint in Tyre and began to import an inferior silver coinage from the Far East consisting of 80% pure silver.
The Religious leaders in Israel, realizing that the new coinage was not sufficiently pure to fulfil the Commandment of giving the Holy Half-Shekel appealed to the Emperor for permission to produce a ceremonial coin of sufficient purity to fulfil our religious obligations. The Rabbanim received special dispensation to produce the requisite coinage on condition that they continue with the motif of the Tyrian Shekel, so as not to arouse objections within the Roman Empire that the Jews were granted "autonomy" to mint their own coinage.
Now the Rabbanim in the year 19/18 BCE had a serious problem. On the one hand, the giving of the Holy Half-Shekel is a Torah Commandment. The problem arises with the motif of the Tyrian Shekel. On the obverse appears the image of Melkhart, known to us as Hercules, the god of the Phoenicians. On the reverse, appears an eagle on the bow of a ship with the legend: "Tyre the Holy and City of Refuge", and the date of issue.
Both images, a foreign god (or any likeness of man) and an eagle, are Torah prohibitions. And yet the Rabbanim decided that the importance of the giving of the Holy Half-Shekel superceded the violations incurred in using the Tyrian motif. More than this, these coins were actually brought into the very Beit Hamikdash itself, a vault room full of coins dipicting a foreign god, inside the very Temple. And the sages went as far as issuing the decree, as recorded in the Talmud, that only the Tyrian Shekel was acceptable for fulfilling the Commandment of giving the Holy Half-Shekel (because of its silver purity).
Can you imagine the Rabbanim today producing a religious item and putting on it the image of a foreign god? Unheard of, right? And yet that's exactly what we did. Under Roman Law, we had no choice if we wanted to fulfil the Commandment, and so important was it deemed to do so, that we entered the image of a foriegn god into the Holy Temple, an act that only a few generations before sparked the Maccabean Revolt!
The coins minted in Jerusalem between the years 18 BCE and 65 CE were virtually identical to their predecessors from Tyre with one addition, the letters KP that appear on the reverse on the upper right side. According to Professor Yakov Meshorer, of the Israel Museum, whose research and published findings have opened up the entire world of ancient Israelite coinage, and to whom the whole House of Israel is deeply indebted for bringing us this Torah, the KP may have been an acrostic that stood for "By Authority of the Roman Constitution". (We believe it was actually the world's first Hechsher, and stood for "Kosher for Purim"! Only kidding.)
In the days of the later second Temple we are told in the Talmud, if a person were to pay his/her Half-Shekel with a whole shekel, requiring change, they would give the Temple Treasurer their shekel, and two kalbonot (money changer's fees), and would receive in change a half-shekel.