Ketchup to Moon rock: What's the point of a World Expo?

Expo 2025 kicked off Sunday in the Japanese city of Osaka but in the age of online information and mass tourism, what is the purpose of a World's Fair?

The huge events, which draw millions of visitors to a chosen city every five years or so, hark back to London's 1851 Great Exhibition held inside the Crystal Palace.

As 160 countries and regions show off their technological and cultural achievements at the six-month Osaka Expo, AFP looks at what it's all about:

What is a World Expo?
Expanding on national expositions in Paris at the dawn of the Industrial Revolution, Imperial Britain built an immense glass Crystal Palace to host 14,000 exhibitors from 40 countries.

That marked the start of the Expo phenomenon that over the decades introduced the world to ketchup, the telephone and X-ray machines among myriad other technologies.

The Paris edition of 1889 featured the Eiffel Tower -- intended as a temporary attraction -- and Pablo Picasso's anti-war painting "Guernica" was first shown at one in 1937.

Historically, World's Fairs did not just exhibit new technologies but also included racist displays of actual people from the colonies of the time.

Do we still need Expos?
While World Expos still showcase future technologies, some argue that the advent of the internet, mass media and cheaper foreign travel have made them redundant.

Global turmoil in the form of conflicts and trade wars have also led critics to question the idealistic values of unity and development touted at the events.

But organisers of Expo 2025 in Osaka have stressed that in-person exchanges between nations and the resulting "unexpected encounters" are still important.

"Humans are creatures that have progressed, little by little, by coming together, interacting, and sharing," they said.

Among the dizzying number of displays this year are a meteorite from Mars, a beating "heart" grown from stem cells, and the world's largest wooden architectural structure.

Where are they held?
Since 1928 the Paris-based International Exhibitions Bureau has run the Expos. More than 180 countries are members and the host city is chosen by a vote of its general assembly.

This is Osaka's second World Expo after the 1970 edition -- featuring a Moon rock -- that was attended by 64 million people, a record until Shanghai in 2010.

The United States once held frequent World's Fairs, as they are known there, leaving behind landmarks such as the Space Needle in Seattle and New York City's Unisphere.

But the world's largest economy last hosted one in 1984, with some experts saying their popularity has been overtaken by the Olympic Games and attractions such as Disneyland.

What's in focus at an Expo?
Buildings often take centre stage at World Expos and this year is no exception, with each country dressed to impress.

The Chinese pavilion's design evokes a calligraphy scroll, while the Portuguese one created by Japanese architect Kengo Kuma features ropes that "evoke the movement of the ocean".

"Expos have always acted, and continue to act, as places of architectural experimentation," said Isaac Lopez Cesar from Spain's University of A Coruna.

They offer a forum "where new architectural forms, new materials, new designs and structural typologies, and, in general, new technological advances applied to architecture are tested", he told AFP.

What's the environmental impact?
Themes of sustainability run through the Expo, including at the bauble-like Swiss pavilion, which aims to have the smallest ecological footprint.

But World Expos have been criticised for their temporary nature, and after October Osaka's man-made island will be cleared to make way for a casino resort.

According to Japanese media, only 12.5 percent of the wooden "Grand Ring" -- a vast structure that encircles most of the national pavilions -- will be reused.