Where in Europe are you most likely to see the European Union flag proudly flying above private homes and buildings? The answer is obvious, if strange: the United Kingdom, by citizens who dread the idea of Brexit. Is it really necessary to lose something that we love – and need – before we really begin to appreciate it?

We believe that, as a sign of our common European identity, EU citizens should, starting on 21 March, proudly display the Union banner. In the face of the challenge posed by nationalists and populists ahead of the European Parliament elections in May, standing up for Europe’s fundamental values has never been more important. Flying the EU flag from our homes and offices can send an undeniable signal that the Union will not be hollowed out by its enemies, within or without.

In an era of growing uncertainty, frustration, and obfuscation of our common destiny, too many Europeans seem oblivious to the long history of dislocation and war that preceded the creation of the EU, and the unprecedented period of peace and prosperity that we have achieved since the 1950s. For 70 years, Europe’s shared institutions have underpinned the common market, the euro, and the vigorous expansion of individual rights under the protection of the European Court of Justice.

Moreover, the European welfare-state model is a beacon of civilisation and an example for the entire world. The incorporation of the Charter of Fundamental Rights in the Treaty of Lisbon crowned the construction of an integrated area of 500 million people based on democracy, the rule of law, and the highest affirmation of human dignity. When we travel with our common EU passport, we are recognized and respected worldwide as citizens of a key player in the world order.

These achievements are under threat not only from the Union’s internal opponents but also by the contempt shown for the EU – indeed, for all multilateral institutions – by US President Donald J. Trump’s administration. The institutions that have long underpinned peace, security, and the growth of world trade are, for Trump, enemies to be undermined, which is particularly dangerous given the confrontation between the United States and China. Today, the Sino-American feud is disrupting world trade; tomorrow, it may be world peace.

There is little doubt that we in Europe will be unable to preserve what we have achieved over the past seven decades if each EU member state strikes out on its own. After all, even the largest EU member, Germany, is a minnow compared to the US and China. Alone, none of us can manage the enormous challenges posed by technology, protectionism, climate change, or international terrorism.

But instead of recognizing that Europe’s strength is its unity, nationalistic and xenophobic forces have gained support across the continent by promising to close our frontiers, dismantle free movement, and reassert our national control over all public policies. The dramatic increase in migration inflows, owing largely to the Syrian Civil War and the near-anarchy prevailing in Libya, have created fertile ground for xenophobes to spread their message of hate. Exploiting the insecurity felt by low-skilled workers and the unemployed, they blame immigrants for all of Europe’s woes. Yet, given Europe’s demography, increasing inflows of skilled migrants are needed to preserve our economies’ dynamism and the sustainability of our health and pension systems.

Yes, Europe’s institutions and policies need deep changes to reconnect with disenchanted citizens. We must show again a capacity to foster growth and investment, to meet the challenges of fast-changing technologies and climate change, and to revitalise our faltering social model. We must show that our common institutions are able and willing to listen to the demands of a frightened public and that we can act together to protect our frontiers and bring greater security to our unstable eastern and southern neighbourhoods.

But there is also an urgent need to mobilize European public opinion around a symbol of our unity and our future projects: and that symbol is the European flag. For this reason, in January one of us launched the idea that starting on 21 March, we display the flag on houses, factories, and offices.

21 March is the first day of spring, and we would like to believe that the coming European elections will herald a new spring for the European project. The date is also the anniversary of the death of Benedict, patron saint of Europe. In one of the darkest hours of the demise of the Roman Empire, Benedict issued a stirring call for tolerance and piety to rebuild a sense of community in the face of nihilism and barbarism.

Let us show our flag to the world, as the symbol of our unity and our dreams, and as a sign of a new beginning in our efforts to preserve and deepen European unity. Or will we recognize what we have only when it is too late?