By Katya Adler BBC Spain correspondent

The forum hopes to be a hive of ideas

Spain's King Juan Carlos inaugurated the event at the city's especially-refurbished waterfront.

Organisers say they expect more than five million visitors to the 2004 Forum of Cultures.

It is being promoted as part-festival, part meeting-of-minds on broad themes such as peace, cultural diversity and sustainable development.

Countless conferences and cultural exhibits are planned.

Star guests

The Dalai Lama has been invited, as has the former Soviet president Mikhail Gorbachev.

There will be performances of a different kind too: Dance and theatre festivals and more than 400 concerts, hosting a string of international celebrities.

The Forum's organisers describe it as a "cultural Olympics".

But critics say it is a sham.

Hundreds of millions of dollars have been spent on the event

The anti-globalisation group, the Assembly of Resistance to the Forum, says the event cynically uses the concepts of peace and diversity to earn more money from tourists.

Barcelona's Federation of Neighbourhood Associations says it has taken priority over more immediate urban issues such as health care and housing.

The Forum's events are being funded with around $460m of public and private money.

And $2.6bn has been spent on infrastructure, including the transformation of Barcelona's once crime-ridden northern shore.