Relics of the true cross are a strange thing, and carry with them a Christian legend most Christians have never heard of.
Known as the "Golden Legend," it begins as Adam—as in Adam and Eve—lays dying. Adam asks his son Seth to go the archangel Michael to get a seed from the tree of life. Seth does so, places the seed in his fathers mouth and buries him. A tree grows from this seed, and the tree is chopped down and used in a sacred bridge, which Queen Sheba crossed to visit King Solomon. Eventually the wood from the bridge is used in the crucifix on which Jesus is said to be crucified, thus completing a line from Adam to Jesus.
The first pieces of the true cross are said to have been found some 300 years after his death by the mother of Roman emperor Constantine, the first Christian emperor. They were kept as treasures of the Eastern Roman empire, but after Constantinople (aka Byzantium, and today Istanbul) was sacked in the forth crusade in 1204 the "true cross" was divvied up into smaller pieces "with other very precious relics among the knights; later, after their return to the homeland, it was donated to churches and monasteries." (From Chronica regia Coloniensis.)
However, as having a piece of the cross was good for business, by the end of the Middle Ages so many churches had claimed to possess a piece of the true cross, that in John Calvin's (of Calvinism) words "there was enough wood in them to fill a ship."
Igreja de Vera Cruz de Marmelar or "Church of the True Cross of Malamar" in Portugal is one such church to still hold claim to a piece of the true cross. (Other churches holding a piece of the 'true cross' include Santo Toribio de Liébana in Spain, the Schatzkammer in Vienna, the Church of the Holy Sepulchre in Jerusalem, Premonstratensian Abbey in Switzerland, and Notre Dame in Paris.)
However the Igreja de Vera Cruz de Marmelar may use the piece of the cross in a much more active way the any of these other churches. According to a local, the church is "a place where exorcisms are still carried out on a regular basis, with the help of a small piece of the Holy Cross. Even non-believers admit to a very strange 'vibe' around this large church in a small town."
Believed by locals to create miracles, the piece of the cross is taken through the streets in procession each year, and the cross is believed to help in healing psychological and spiritual disorders.