In an exhibition entitled "Picasso: Tradition and Vanguard", Spain's Prado and Reina Sofia museums began exhibiting more than 100 pieces by Pablo Picasso alongside the works of the 17th and 18th century masters who influenced him most, namely Diego Velazquez and Francisco de Goya. The exhibition, expected to be the cultural highlight of the Summer in Madrid, was organised to commemorate the 25th anniver­sary of the arrival of Picasso's most famed work, Guernica, in Spain from the US in 1981 following the country's return to democracy after the end of' the dictatorship of Generalissimo Francisco Franco.

"It's a demanding retrospective of the most important artist of the 20^th century," said Prado director Miguel Zugaza. "An exceptional collection which has rarely been seen and will be very difficult to bring together again in the future." The show also celebrates the 125th anniversary of the artist's birth. Born in Malaga , Picasso died in Paris in 1973.

"It's not enough to describe it as a great exhibition," one of the show's curators, Francisco Calvo Serraller, told reporters in a pre-launch presentation last week. "It's inconceivable, unheard of, a historic event which transcends art and demonstrates how the tragedies of war were reflected in Spain ."

The Prado, normally dedicated to pre-19th century artworks, has given over its elegant central art gallery to contrasting Picasso's artworks with that of painters he credited as being his inspirational mentors. The star attractions at the Prado will be comparisons between Velazquez's 1656 Las Meninas and Picasso's black, grey and white versions of the work from the 1950s. Several metres away are Picasso's versions of Goya's The Naked Maja (1797). Ten minutes down Madrid 's tree-lined Paseo del Prado is the Museo Nacional Centro de Arte Reina Sofia . Here, the second part of the exhibition focuses on the giant, anti-war canvas Guernica , that Picasso painted after the indiscriminate 1937 air bombing and machine-gunning by Franco's German allies of the small Basque town of the same name.

Nearby are Goya's oil painting The Shootings of May 3rd and Manet's Execution of Emperor Maximilian.

The show details Picasso's evolution from his blue period to cubism, as well as his relationship with surrealism, includes other prized works such as Massacre of Korea, from the Picasso museum in Paris, and Three Musicians, from the Philadelphia Museum of Art. The latter has never been exhibited in Spain and was last seen in Europe some 40 years ago.