For the Jews of Belgium, Wednesday should have been the happiest day on the calendar.

Purim, normally the most raucous and joyful Jewish holiday, began Wednesday at sundown. But this year, there was no merriment in Brussels. The day after terrorist attacks killed at least 31 people and injured 270 more, Jewish congregations in Brussels decided that celebrating Purim would not be appropriate — or safe.

But their counterparts in Paris, who saw the horrors of terrorism just months earlier, went on with their annual celebrations, determined to show their spirit is unbroken.

The holiday, which celebrates the Jewish people’s survival when the tyrant Haman vowed to wipe them out, is normally marked with festivities including costumes, sweets, dramatic productions and alcohol.

The Great Synagogue of Europe, located in Brussels’ historic heart, had planned a rock concert for hundreds of attendees. But the concert, along with other events, was canceled. Asking hundreds of Jews to leave their homes to celebrate Purim on Wednesday night was considered to be too much of a risk.

“In general, we have to be careful. Every day, every service, morning and evening,” a staff member at the Great Synagogue said Wednesday. The synagogue employee, who did not want to give his name, said that his congregation and at least four others decided, after conversations with Belgian authorities, to cancel their Purim parties.

In Paris, on the other hand, Jews were mindful of the tragic attacks in neighboring Belgium — and decided that the best way to stand up to terrorism would be to celebrate all the more.

“Purim is very related to what is happening in the world, in Paris a few months ago or this week in Belgium,” said Jacques Canet, president of the Great Synagogue of Paris. “We have a habit to say that Haman is still existing. And the best way to fight Haman is to celebrate Purim with hamentaschen cookies, with joy, with music. This is the best way to fight the Hamans of today.”

The Paris congregation was open, with extra security at its doors, Canet said. “The central synagogue in Paris is about 150 years old. It’s never been closed to anyone, whatever the circumstances were. Even during World War II it remained open all along,” he said. When Paris was attacked last year, he said, “We made the decision to remain open, whatever was happening around us.”

On Wednesday, the day after terrorists struck close to home again, at least 500 people came to the Paris Purim service — more than any year before, Canet said.

The observance in Brussels was much more sober, just a quiet worship service to read the Book of Esther, which tells the Purim story. The employee at the Great Synagogue said about 50 to 70 congregants were expected to attend, whereas most people in the 400-family congregation would have come to the rock concert.

Long before Tuesday’s attacks, Belgium’s Jewish population of roughly 30,000 people had been anxious about a resurgence of anti-Semitism in Europe. At the Great Synagogue, anyone who is not a regular attendee must show a passport to get inside the building — a precaution that has become so matter of course for European Jews that some are surprised to hear American Jews don’t require IDs to enter their synagogues.

Purim will not bring any relief with its silly costumes this year, the synagogue staffer lamented. “In the street now, it’s dangerous to walk with a kippah in the street.”

This post has been updated.

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