'It's our duty to turn the migration challenge into an opportunity'

The refugee crisis that took Europe by surprise last year has posed many challenges for the EU's asylum system, border management and decision-making.

But it is cities that have borne the brunt of the arrival of more than 1 million people in a single year.

Roughly 70 percent of the European population and 75 percent of the continent's jobs are concentrated in cities. Many of the problems governments have to address – from affordable housing and air quality to energy efficiency an...