The church is a still-unfinished modernist masterpiece by architect Antoni Gaudi that was visited by nearly five million people last year.The pope's visit during a week-long trip to Spain coincides with the 100th anniversary of Gaudi's death on June 10, 1926.The devout Catholic, whose cause for sainthood is advancing in the Vatican, was hit by a tram while on his way to pray at a church.Pope Leo flew to Spain on Saturday, starting his visit in Madrid where he gave an unprecedented speech to the Spanish parliament and held an open-air mass with 1.5 million people.During his visit, the US-born leader of the world's 1.4 billion Catholics has denounced polarisation and called for "patient dialogue" instead of war and rearmament.He has also sought to reinvigorate the Church in a traditional Catholic bastion where religious observance has declined sharply and has promised the Church will do more to tackle what he called the "scourge" of sexual violence by clergy.After Barcelona, he visits the Canary Islands on Thursday and Friday where he will focus on immigration as the Atlantic archipelago is a key entry point to Europe for irregular migrants.Before the Sagrada Familia mass on Wednesday, he is due to visit a prison and an abbey in the Montserrat mountain range overlooking Barcelona.Completion challengeThe Sagrada Familia's soaring central Jesus Christ tower was only completed in February, bringing the basilica to its maximum height of 172.5 metres (566 feet).The peak deliberately falls short of the 177 metres of Barcelona's Montjuic hill -- an act of religious respect from Gaudi who believed the hill was the work of God.