Saints as intercessors
The veneration of saints is as old as the Christian church itself. Christians believed that saints could intercede for them with God. Of couse many still do. Where saints were buried, people gathered to celebrate the anniversary of their death. On this foundation an elaborate system developed during the Middle Ages. For specific complaints or dangers people would ask help from a specific saint.
Agatha of Catania
The city prefect tried to force Agatha to have sex with him. In this way she could have escaped punishment for being a Christian. She declined his offer, and he sent her off to a brothel. There she refused to serve customers. As punishment, her breasts were cut off. Agatha protects against breast cancer and she helps rape victims. She is also invoked against earthquakes and volcanic eruptions.
Agnes of Rome
She too preferred death to losing her viginity. Her main attribute is a lamb, probably because her name Agnes resembles the latin word for lamb agnus. Betrothed couples ask her for protection, and so do rape victims.
A deaconess in Alexandria. She refused to renounce Christ and her teeth were broken during torture. They threatened to burn her if she persisted. She didn't wait, but jumped into the fire herself. She protects against toothaches and is patroness of dentists.
Ursula of Cologne
According to one of the versions of her life story saint Ursula was martyred by the Huns together with 11,000 other girls and women. Saint Ursula became patron of Catholic education, especially of girls. The order of the Ursulines established many schools.
The death by stoning of Stephen is told in the Acts of the Apostles. He was the first man to shed his blood for his belief in Jesus. Saul (St. Paul) was one of the witnesses. Stephen's patronage includes those who suffer from headaches, but also stone masons.
Saint Barbara was locked up in a tower by her own father because of her disobedience. She escaped but was caught again. Her father then killed her. Thereupon he was instantly struck by lightning. Saint Barbara became patroness to all kinds of builders, not just to those who make towers. She also protects against lightning, explosions and death by artillery.
Sebastian survived the arrows of his torturers. Later he was clubbed to death. He became patron of archers and arrowsmiths. He was also one of the "Pestheiligen", saints who protect against the plague. This disease seemed to cause death in a random way, like the arrows of archers. Sebastian survived shotwounds, so to the medieval mind it seemed logical he would help against attacks by the Black Death.
Catharine of Alexandria
Saint Catherine survived torture on the wheel, because it broke. It injured many bystanders. She was then killed by the sword. She triumphed over the emperor Maxentius, who is often depicted lying at her feet. The association with a wheel made Catherine patroness of spinsters; her learning was recognized by librarians; her debating skills made her popular among lawyers.