Five years ago, on 14 March 2011, the cities of Aleppo and Damascus witnessed a rare sight: hundreds of people on the streets, calling for democratic reforms and the release of political prisoners in Syria.
None of those who marched that Monday - indeed, no one on earth - could have foreseen what the next 60 months would bring. Today, Syria lies in ruins. It has been emptied of nearly a quarter of its population. Of those who remain, 13.5 million rely on aid, and 6.6 million are homeless. A whole generation of children has grown up knowing nothing but war and exile.
Such are the consequences of a conflict that has claimed and maimed hundreds of thousands of lives since its beginning. The sheer magnitude of the Syria crisis - the effects of which spilled dramatically onto European shores last year - beggars belief. It has uprooted an average of 50 families every hour of every day since 2011, and generated the biggest humanitarian and refugee emergencies since the 1940s. More than a century's worth of progress in establishing laws and norms governing the conduct of war has been rolled back.
But what is even more shocking is that states with the power and responsibility to end the conflict have remained resolutely intent on prolonging it. Far from pressing for peace in Syria, they have sent planes and troops into the country, armed and trained the belligerents, provided them with diplomatic and political cover, and turned a blind eye to the most egregious violations of basic international humanitarian law.
The rank pessimism surrounding the current 'cessation of hostilities' in the country is the product of all of this. It is a scandal that it has taken five years for the warring parties and their backers to agree to an initiative of such limited scope, and an indictment of their intransigence and bad faith since 2011 that hopes for its holding - and for a wider settlement in Syria - are so slim.
For while the current lull has offered some fragile respite to innocents in certain parts of Syria, belligerents have up until now enjoyed completely free rein in bombarding densely populated areas, laying waste to schools, hospitals and homes, and deliberately and wantonly attacking civilians and civilian infrastructure, notwithstanding commitments made at international gatherings in Geneva, Vienna and Munich. Seventy-two hours after an earlier, ill-fated truce was agreed last month, airstrikes hit medical facilities in northern and southern Syria, including several supported by my organisation, the International Rescue Committee (IRC).
Depressingly, a series of UN Security Council resolutions demanding an end to such barbaric conduct have proved nothing more than a false dawn. The Council's members have miserably failed to stay the hand of those bent on destroying civilian life in Syria, or to pressure regional powers to hold their clients accountable. As a result, the Council's credibility as the final arbiter of international peace and security has been eroded, perhaps irreparably, and the situation inside Syria has gotten worse, not better. To take just one marker, the UN puts the current number of Syrians who, owing to violence, insecurity and bureaucracy, can access only some of the aid they need some of the time at 4.6 million, an increase of more a third since February 2014, when the first resolution was adopted. The number of people completely under siege - deliberately starved of food, water and medicine - has doubled, to nearly half a million.
The steps necessary to manage the consequences of the conflict are clear. First, governments must deliver on pledges made last month in London to fund the UN's aid appeals for Syria and the region, and pressure less generous countries to join them in alleviating the humanitarian emergency there.
Second, the top-level commitments by Syria's neighbours, international donors, and multilateral development institutions to get some of the almost five million Syrian refugees in the Middle East into employment - and their children into education - must be worked through and implemented as quickly and as efficiently as possible.
Third, Lebanon, Jordan, Turkey and Iraq must ensure that their borders are open to those fleeing the violence. And fourth, countries outside the region must massively scale up the resettlement of vulnerable refugees from these states.
The European Union, which saw half a million desperate Syrians make for its borders by boat last year, has a particularly urgent role to play here, in widening safe and legal routes to and through the bloc for asylum-seekers, and significantly improving conditions on Lesbos and the other gateway islands in the Aegean. So does the United States, which has committed to take in just 10,000 Syrian refugees this year: 100,000 would be a far more fitting American commitment.
Ultimately, however, such support and initiatives will still only deal with the fallout from this crisis, not its causes. That will require states with sway in Syria finally bringing pressure to bear on all those who continue to flout international humanitarian law, and working together to generate a durable solution to the conflict.
The prospects are not auspicious. One of the IRC's aid workers in Syria, a 26-year-old ex-restaurant employee from Aleppo, lamenting the international community's failure to act recently remarked: "Today, when Syrians say goodbye to their families, they know it might be for the last time." Five years of war could easily become 15, as in Lebanon, or 50, as in Israel-Palestine, which passed that grim milestone in 1998. In time, history will deliver its verdict on how the world responded to the war. But my colleague, and the Syrian people - whose exodus from their homeland shows no signs of abating - have already delivered theirs.