A year ago, European leaders gathered in Brussels to create a single supervisor to oversee the region’s systemically important banks. This momentous step is nearing completion. But it is only one stage in an even more ambitious undertaking: the building of a banking union for Europe.

The German government was among the first to float the notion of a European supervisor as a way to combat the destructive synergies between strained banks and indebted states in the eurozone. Today, more than ever, I see a banking union covering supervision, resolution, fiscal backstops and rules for deposit insurance as an urgent necessity.

The merits of a banking union are rarely disputed. But there is a debate about how to shape its governance and accountability; and about what we can deliver in the short term and what our ultimate goals should be.