According to Christianity, Holy Week (or "passion week") is the last week of Lent and the week before Resurrection Sunday. It begins on Palm Sunday, and also includes Maundy Thursday and Good Friday. During Holy Week, the events of Christ's passion are commemorated, including His Last Supper, betrayal and crucifixion. It is used to commemorate the Passion of Christ.
Jesus died on the cross and was buried before sunset. So Friday was first day that Jesus lay in the tomb. In most churches, the decorations are red to symbolize the blood of martyrdom. Some churches remove all decorations on Good Friday, veiling anything that can’t be removed in black. 
Holy Week is one of the most important parts of the Christian year, particularly for Roman Catholics, and sees elaborate celebrations in many parts of the world including Italy, Spain, Mexico, and other countries in Latin America. Semana Santa has been one of the most important celebrations in Seville, Spain for centuries (like in other places in the world, i.e. Tarma, Peru, Marinduque, Italy, Popayan, Colombia, Iztapalapa, Mexico City, Malaga and Gerona, in Spain). It may have its origin as far back as the 14th century.
Hans Holbein the Elder, The Agony in the Garden.
Hieronymus Bosch, Ecce Homo.
Rubens, The Crucified Christ.
Annibale Carracci, The Holy Women at the Tomb of Christ.
Rembrandt, The Last Supper, after Leonardo da Vinci's famous mural.