Four months ago a German court saved a controversial sculpture from being judicially removed, subject to appeal. The carving is located four metres high in the outer wall of a church in the town of Wittenberg, and depicts a group of Jews sucking the teats of a pig, while a rabbi inspects its anus. The intention of the medieval stonemason — the piece is dated to around 1305 — was not flattering, to say the least and this motif was sufficiently widespread in Northern Europe to have a name — the Judensau. There are at least a couple of dozen examples, mostly incorporated into churches or cathedrals, from Uppsala in Sweden to Vienna.

If you didn’t know about the insult — that Jews as a people were filthy and hypocritical enough to become almost intimate with an animal regarded as dirty by everybody and inedible by Jews themselves — the chances are that you wouldn’t guess what a Judensau was unless you were told. But, of course, many Jews do know, and if you didn’t before then you do now.

The one on the Stadtkirche in Wittenberg has particular resonance because of its association with that father of Christian schism, Martin Luther. The author of (among other works) The Jews And Their Lies, who called for synagogues to be destroyed, Luther was specifically romanced by the Wittenberg Judensau. In 1543 he described the sculpture in detail, describing the sculpted rabbi as looking into the pig’s Talmud.

Unsurprisingly then, all of the Judensau depictions in what is now Germany are highly problematic and the Wittenberg version more than most. In 1988 the authorities placed a commemorative plaque in the ground beneath the sculpture linking the antisemitism that motivated it to the eventual murders of six million in the Holocaust. The plaque and its accompanying information board is, naturally, much more accessible than the Judensau itself.

The case for the Judensau’s removal to a museum was made on the grounds that it was insulting and defamatory to Jews. The court’s contrary ruling was given on the basis that, according to the judge, “anyone looking at the relief cannot fail to see the memorial and the information sign the parish put up in 1988”. The pastor of the Stadtkirche to whom the Judensau was “repulsive and tasteless” talked of trying to handle this unwanted inheritance responsibly and said he was in talks with the German Central Council of Jews on how to update the memorial plaque.

Just in case we are inclined to become all Anglo-smug about this controversy, we have our own awkward history. The one I know best is in Lincoln cathedral — the shrine of Little St Hugh, the supposed victim in the medieval blood libel that cost many Jews their lives in the 13th century. This is Chaucer’s “Yonge Hugh of Lincoln, sleyn also with cursed Jews”. In 1999 when I visited, the plaque by the shrine had a brief mention of the blood libel and asked for forgiveness.

But at the door of the cathedral I picked up a copy of the Cathedral Community Quarterly, with an article by the then Bishop of Lincoln, in which he praised the early Christians for taking over history, “superseding Jewry” and challenging the Roman Empire. On the way down Lincoln’s famous Steep Hill you pass the medieval pairing of Jews Court and Jews House. On one, a plaque reads: “Owned by a member of the Jewish community in 1290”. It doesn’t tell you that in the same year the Jews of England were expelled. We probably don’t have Judensau sculptures in England simply because there were no Jews to insult.

To me, in the end, contextualisation is almost everything. The remaining Judensaus are hugely important, very old and relatively rare reminders of Christianity’s often hidden past, as well as being examples of medieval art. So keep them and explain them. In so doing you make a better job of reparation and of guarding against future atrocity than you do by ignoring them, briefly acknowledging them or removing them.

Slavery, mass murder and persecution punctuate human history and what is important is the willingness to face up to the truth. Few memorials work better than the stolpersteine in so many European cities now, marking the names and domiciles of Jews taken from their homes and murdered. And more towns should do what the city of Graz in Austria has done, placing information boards in public places showing photographs of the same place from the same aspect in Nazi times, adorned with swastikas and marching storm-troopers. No wonder Graz has been such a poor stamping ground for the new far right. Because it says: this is what we were; let us never be that again.

David Aaronovitch is a columnist for The Times