SPANISH writer Javier Sierra has at least one thing in common with famed inventor and artist Leonardo da Vinci in that he has a sense of unquenchable curiosity and the will to challenge widely accepted ideas.

"I keep observing the world with a child's eye and I am sure that many of the 'official versions' of history that we study in school are, to say the least, questionable," said Sierra, who was in Shanghai recently to give a lecture.

Sierra was born in 1971 in Teruel, Aragon, Spain. He is a journalist, writer and researcher who studied journalism at the Universidad Complutense de Madrid. He is editor consultant of the monthly magazine Mas Alla de la Ciencia (Beyond Science), distributed in Spain and Latin America. During the last few years he has concentrated on writing about purported ancient mysteries.

He is considered one of the most outstanding authors in the Spanish literary scene. His first book was published in 1995.

His 2006 novel "The Secret Supper" was in the top 10 of The New York Times Bestseller list and has been published in 42 countries. More than 3 million copies have been sold.

He is obsessed with occultism, enigmas and intriguing facts that are controversial and unexplained or clarified by experts. He calls them the "black holes" of history and he hopes to locate them.

He said he raised questions in his articles when he worked at the magazine and he once published two nonfiction books about historical and scientific mysteries. Even if he did his best to reveal unexplained facts to his readers, he could not propose answers without entering the dangerous field of speculation.

This is how the idea of "The Secret Supper" originated, he explained.

"With literature, things are essentially different," Sierra says. "I can use facts as a sound basis for my novels, and my imagination to explain those unsolved mysteries that historians cannot clarify."

Sierra said he does a lot of research and looks at numerous historical documents and books while probing mysteries. He said he has visited more than 20 countries including Egypt, Italy and Turkey while doing research for his books.

He "investigates" the truth and builds his own criteria regarding what happened as he searches for answers. His books are based on real documentation and extensive field research.

He said da Vinci fascinates him.

There is no shortage of materials about da Vinci, but people don't know much about his thoughts, he said.

Sierra said he believes da Vinci was open to outlandish ideas, including those of the Cathars, a heretical Christian sect, and this was very rare among artists in his time.

Da Vinci approached forbidden books and paid attention to marginalized figures in the Bible, which aroused Sierra's curiosity, he said.

Sierra believed the Louvre version of da Vinci's painting "The Virgin of the Rocks" suggested the artist agreed with some heretical ideas as the piece blurred the roles of the Christ Child and the infant John the Baptist.

Da Vinci's paintings have some political metaphors, Sierra said.

"The Secret Supper" is a historical thriller set in 1497. Sierra said it depicts a deadly game of wits between da Vinci and Father Agostino Leyre, a Dominican Inquisitor and expert on the interpretation of secret messages, who is ordered to supervise da Vinci's final touches to his masterpiece "The Last Supper." Leyre is intent upon bringing da Vinci to trial for heresy. Sierra said the book gives you his thoughts on da Vinci's best-known religious work and keeps you guessing until the final page.

Sierra's lecture in Jing'an District was interlocked with intriguing myths, secrets and mysteries.

He talked about the route of the "Poor Knights of Christ and the Temple of Solomon," and unexplained secrets like maze-shaped churches, stones featuring the image of knights and mysterious symbols.

Sierra gave his own interpretation of art works, such as "Las Meninas" (The Maids of Honor), a 1656 painting by Diego Velazquez, the leading artist of the Spanish Golden Age.

The painting shows a large room in the Madrid palace of King Philip IV with several people. The young Infanta Margarita is surrounded by her entourage of maids of honor, chaperone, bodyguard, two dwarfs and a dog. Just behind them, Velazquez portrays himself working at a large canvas.

The work's complex and enigmatic composition raises questions about reality and illusion, and creates an uncertain relationship between the viewer and the figures depicted.

Sierra found that if linking all the figures in the painting in lines, a Capricorn shape will emerge, and the queen, Mariana of Austria, was a Capricorn. He believed Velazquez was using art to pray for an heir to the throne because the queen hadn't given birth to a boy at that time.

Sierra said he has many interesting theories such as, "the best way to hide a secret is to put it right before your eyes" and "a painting hides a story, which may challenge what we have believed for a long time."

In times when printing technology did not exist, paintings were used to tell a piece of history, a story or hide secrets, few were purely for decoration, he said.

"You can only understand the meaning of a painting when you know where and under which circumstances it was created," Sierra said.

It took him three years to complete "The Secret Supper."

"When I went to see 'The Last Supper' in Milan, I was surprised because that painting was created as a sort of game of illusion for the human eye," he recalled.

Leonardo wanted to confound the observer by painting portraits of ordinary men, not saints, he said.

"It was difficult for me to distinguish between what was actually on that wall at the convent of Santa Maria delle Grazie, and what should have been."

He visited the monastery of Santa Maria delle Grazie in Milan, Italy, to see "the Last Supper." Each visitor is allowed about 15 minutes to see it, according to regulations in an attempt to protect the mural. Sierra bought tickets several times a day, and he said he aroused the suspicion of a security guard, who suspected him as a terrorist or a mentally disturbed individual.

"It was the most difficult part in writing the book," he joked.

Da Vinci was believed to be a master in "playing tricks" in paintings.

Sierra said he would be happy if 100 years later, more manuscripts about da Vinci are found and they prove his theories.

He revealed that his next work will be about the space program, but kept the plot a secret, which makes perfect sense.