Pilgrim badges are decorations worn by some of those who undertake a Christian pilgrimage to a place considered holy by the Church. They became very popular among Catholics in the later medieval period. Typically made of lead alloy, they were sold as souvenirs at sites of Christian pilgrimage and bear imagery relating to the saint venerated there. The production of pilgrim badges flourished in the Middle Ages in Europe, particularly in the 14th and 15th centuries, but declined after the Protestant Reformation of the mid-16th century. Tens of thousands have been found since the mid-19th century, predominantly in rivers. Together they form the largest corpus of medieval art objects to survive to us today.