NATO has been building a new headquarters in a suburb of Brussels, Belgium, which now looks like it will wind up costing $1.5 billion or more.

Why? 

You might think that, what with the Warsaw Pact having been disbanded on February 25, 1991, NATO might be looking to shed office space, not build itself a bigger monument. But, according to NATO:

The new NATO Headquarters will be a secure, collaborative network-enabled capability supporting NATO business for you and for future generations. 

Well, that clears a lot of questions up.

The construction of the new NATO Headquarters started in October 2010 and is planned to be completed early 2016. NATO will start to move immediately after completion.

"Flexibility" is the key word:

The design of the new headquarters provides flexibility to NATO. 

The new building will be able to accommodate NATO's changing requirements into the future as the design and the standard fit-out allows for a configurable use of the building. 

The design of the building, using standard components which provide additional flexibility for the future. 

The new building will enable all Allies to have the space they require and there is also space for expansion should the need arise.