Leading article: A landmark for London

After months of anxious planning, the elegantly undulating roof of the London Aquatics Centre has been successfully lowered into place. It is not only an inspiring sight, but it marks two significant and cheering developments.

The first is the progress that it signifies in the preparation of the Olympic Park. With each week that goes by, the pessimists who doubted that the vast site would be ready in time seem more likely to be proved wrong. The park is coming on apace – and it is not yet 2010.

The second is that the capital is now well on its way to having its first landmark building by Zaha Hadid. The designs of this Iraqi-born British architect, spare and gorgeous at once, have routinely been rejected as too technically ambitious and too expensive. But this also reflects a lamentable national timidity where aspirational public architecture is concerned.

May the London Aquatics Centre usher in a new, more adventurous, age.