The anniversary of the September 11 terrorist attacks on the World Trade Center and the Pentagon will continue to dominate the media and our thoughts over the next few days.
The 'what were you doing when you heard' question will be well rehearsed around the world as we relive and reabsorb those terrible sights. Feelings of sickness and despair will flood back as we try to imagine what it must have been like for those at the scene.
NCE's 'Unthinkable' headline still stands 12 months on.
Despite the vast amount of investigation, explanation and analysis over the last year, the events we witnessed that day are still so far outside our realm of expectation that, looking back, it is often easy to think 'did that really happen?'.
Not, of course, for those who lost family and friends in the tragedy, those who have spent the past year working around the clock to clear the site or those who have been helping to rebuild lives, buildings or businesses. For these people the world will never be the same again.
This week NCE has tried to steer clear of yet more analysis and reflection on the events in New York and Washington a year ago. Instead we have attempted to explain and analyse how the civil and structural engineering profession has responded and learnt from the experiences.
For it is the way that the profession helps to lead society out of post 9.11 trauma that is important.
The key tasks for the profession relate more to generating public and client confidence in infrastructure. This tragedy was a very rare, very extreme event and we must make sure that this fact is kept in mind.
But we live in an uncertain world where, regardless of our best intentions, the 'unthinkable' is never too far away.
So while there are certainly lessons to be learnt about structural robustness, emergency preparedness and about quality of construction, the key task for the professionals all over the world is to take the actions necessary to ensure that people still feel safe.
As a single event, the magnitude of the WTC collapses sets it apart. It is a sobering thought, for example, that during the 12 months since the WTC attacks as many people were killed on UK roads as perished in Manhattan. Ten times more were lost on US highways. To deliver efficient, cost effective and attractive infrastructure, engineers must continue to make compromises and balance out the risks.
There are parallels with many other infrastructure disasters reported by NCE. Whether it is the King's Cross Underground fire or the Hatfield train crash, it is vital that we do not exacerbate the problem by overreacting and scaring the public away from infrastructure.
So has the world changed forever since September 11 2001?
In reality, probably not. Society still needs and uses tall buildings, aircraft and underground railways.
Yet the date will forever remind us how fragile our lives are and how easily plans can be rearranged. For engineers it should also be a reminder of the faith society puts in us to keep them safe. Whatever 'unthinkable' events happen in the future, we must continue to assure them that they are.
Antony Oliver is the editor of NCE