The magnificent Belm Tower on the bank of the river Tagus is one of Portugal's most potent symbol. It celebrates the country's discovery of new sea routes and, in particular, Vasco da Gama's voyage which opened the sea route to India. As the 500th anniversary of this historic journey draws near it has provided a theme for the forthcoming Expo '98 which opens in Lisbon on May 22nd and runs until the end of September.

Expo '98 has been nine years in the planning and was given an added impetus when the UN General Assembly proclaimed l998 as the International Year of the Oceans. The exposition is being presented under the title "The Oceans, A Heritage of the Future", and more than 130 countries and international organisations are participating. Each country has been asked to interpret and present an oceanic theme, not only from an environmental point of view but also regarding the oceans many uses, industrial, mining, exploration and futuristic.

Ireland is the only EU State not participating, a decision that has surprised and disappointed the organisers. "We were most anxious that Ireland participated, particularly with its close links to the sea and its buoyant economy," says Toms Pereira, spokesperson for Expo '98.

Major roadworks, extended national and international rail links, a new railway station, a 13km bridge over the Tagus, a marina, and a facelift for the city are some of the manifestations of this massive event. Expo '98 is more than a promotional occasion. It is a two-pronged development under the management of the state- controlled private company, Parque Expo 98, which is also responsible for administering a massive urban renewal project called Expo Urbe.

When the participating countries pull up stakes and depart, a new residential and commercial complex will stretch along five kilometres of the Tagus river. Hailed as the greatest urban renewal project seen in Portugal, it intends to bring life back to the river, establishing 10,000 new homes and a population of 25,000 by the time the development is complete in 2009.

At the headquarters of Expo '98, a colourful, miniature replica of the forthcoming exposition gives an impression of the finished scenario. But a visit to the site demonstrates its vast scale.

"Lisbon has not been developed in such a way since the earthquake of 1755," explains Mr Toms Pereira, driving his jeep over a rutted, moonscape surface where skeletal shapes of brick, wood and steel are emerging. "It is a clogged city and for a project of this scale it was necessary to go to the outskirts where there was space to develop from scratch."

The costs of staging such a high-profile event are expensive and creeping upwards. The fund source for Expo '98 is 295 billion escudos (£1.14 billion). Income tax is not expected to increase as most of the revenue is garnered from other sources. So far, the State has provided only 0.3 per cent of the Expo budget. EU funding came to 8 per cent of the total and real estate sales are hoped to realise 49 per cent of revenue. However, it now appears that the final cost could be higher.

With land still for sale every effort is being made to make the project as attractive as possible for developers. The exposition is expected to attract 8.3 million visitors of whom 3.5 million will be foreign. Luis Hespanha, marketing manager of the Costa de E'Storil tourist board, reports a substantial increase in the number of tour companies buying space in the E'Storil and Cascais seaside resorts which are only a short drive from Lisbon.

Portugal hopes to realise the major tourism benefits after the exhibition is finished. Some 70 per cent of the exposition pavilions will remain and the Oceans Pavilion, a giant aquarium, the most modern in Europe, is expected to attract one million visitors yearly. The International Area where the visiting countries will mount their exhibitions is being designed in modules which are offered free to participants. This gesture gives Expo more freedom to manage the space afterwards when the area converts to a major trade exhibition centre.

Over the past three years the development of Expo '98 has resulted in the employment of about 15,000 people, mostly in construction, with extra jobs expected in the hotel and restaurant trade. When everything is complete all that will remain of the original industrial site will be the tower of the old oil refinery, standing like Belm Tower once did, as a symbol of a new era.

Portugal is using this last exposition of the 20th century to present itself as a modern country, politically stable and progressive.