Fear of the Black Banners

Updated | Catherine De Bolle is waiting, and she is worried. Even before U.S. warnings of a “heightened risk of terrorist attacks” in Europe during the holiday season, the head of Belgium’s Federal Police was bracing for a new wave of assaults in or around Brussels. The city’s immigrant Muslim neighborhoods were staging grounds for last November’s attacks in Paris, which killed 130 people and wounded nearly 500, as well as suicide bombings in March at Brussels Airport and a downtown metro station, which killed 32 and wounded 300 more.

More than eight months after that last attack, Brussels authorities have girded the city with new security measures, starting with heavily armed soldiers guarding the airport—still under repair from the March attack—as well as European Union buildings and the embassies of NATO countries battling the Islamic State militant group (ISIS) in Syria and Iraq. Combat-ready soldiers patrol the city’s central train station and even the narrow winding streets of its quaint, 19th-century shopping and dining districts. Green army trucks and personnel carriers are a