TO MARK the 1700th anniversary of the Edict of Milan, which brought freedom to the Church under the emperor Constantine, the Ecumenical Patriarch, Bartholomew I, visited Pope Francis in Rome and then Milan (15 May). In the Roman Coliseum (until 15 September), there is a substantial exhibition that has transferred from Milan, and in Serbia another is being held at Viminacium.

In the farther reaches of the former Roman Empire, this significant date seems to have passed with little notice, although Anglicans might have been encouraged to observe the feast of Sts Helen and Constantine on 21 May.

This fascinating gallery show, which currently does not even appear on the British Museum's own website of listed exhibitions, is London's contribution, although it seems to have been arranged without much encouragement from the Churches. It is tucked away in a small, inaccessible room off the numismatic gallery, but is well worth seeking.

The exhibition covers the use of coinage in the biblical tradition, with later coins that include a rare example of the first on which Jesus himself is depicted: a gold solidus, minted in Constantinople for Marcian (AD 450-57), seemingly shows a beardless Jesus, with a nimbus cruciger, uniting the Emperor and Empress Pulcheria in marriage (The Hunterian Museum and Art Gallery, University of Glasgow).

Representing Jesus on Byzantine coinage became commonplace after the iconoclastic period, while maintaining a repertory of demi-gods and the like. The obverse of a pre-decimal penny (abbreviated to a "d." for denarius in £. s. d.) depicted Britannia, and to this day Americans remind themselves that they put their trust in God every time they reach for a greenback.

Since the Mosaic Code long predates the introduction of coinage, reckoned to have begun in Lydia (Modern Turkey) around 650 BC and to have spread across the Persian Empire, Israelites therefore first made use of standardised weights and measures from which coinage developed; we should remember that the pound is still both an Imperial measure of weight and a unit of currency.

In the New Testament (and examples of papyri texts from Oxyrhynchus are shown separately), there are fewer passages that relate to money than we might imagine. The shekel, originally a Jewish measurement of weight, and half-shekel occur in Matthew's account of the collection of the drachma (17.24ff.) and in the Lucan parable of the lost coin (Luke 15.8).

As a silver coin, the shekel was produced from about 126 BC at Tyre, and the mint may later have transferred to Jerusalem to provide for the Temple cult, even though one side of it depicted the demi-god Melqart-Hercules; with the AD 66 Revolt, the coin ceased production. Those Churches that claim Judas's 30 pieces of silver among their relics, most usually turn out to hold silver coins from Rhodes. Judas would have been paid off in shekels. Thirty of them are shown here.

In St Mark's Gospel, still held by most to be the earliest written record of the sayings of Jesus, there is an extraordinary altercation with some of the Pharisees and the Herodians in 12.13 and following.

Commentators and expositors, including my namesake, have uniformly explored the passage simply as a way of understanding Church-State relations. "Render unto Caesar the things that are Caesar's." Quite so.

But biblical exegetes often fail to look at the flip side of the coin: one side of the coin held an image of the emperor, but the reverse had a symbol of a deity, such as Fortuna or Diva Faustina, or a provincial emblem. Commonly, the denarius issued under Emperor Tiberius had an image of the emperor on the obverse and, on the other side, one of his mother Livia, part of the cult of the imperial divinity.

Jesus and his disciples would have daily carried in their scrip and scrippage and in their bags and baggage coins bearing the image of an emperor, an earthly suzerain, and symbols of tutelary deities and of local authorities. Religious Jews and early Christians alike felt unhappy about having images of pagan gods on their coinage.

The most extraordinary, and possibly contentious, coin is the unique quarter-shekel in the British Museum's own collection which depicts a seated deity inscribed YHW (or possibly YHD), suggesting that the proscriptions contained in the Ten Commandments were to be observed only by the Israelites among themselves, and not outside Judah.

"Coins and the Bible" runs at the British Museum (Gallery 69a, free entry), Great Russell Street, London WC1, until 20 October 2013. Phone 020 7323 8299.www.britishmuseum.org