The basilica of St. Sernin in Toulouse is dedicated to him; apparently the French say his name differently. South-western France was an important staging area for pilgrims traveling to Santiago de Compostela, the resting place of the relics of St. James. Folks in Toulouse wanted to have an impressive shrine for pilgrims to visit along the way, so they settled on Bishop Saturninus.
Between Saturninus' house and his church stood the main pagan temple in Toulouse. The oracles of the temple had failed to make any predictions for years; some of the priests blamed this failure on theopsychic interference from Saturninus' proximity. [Okay, theopsychic interference is my term, but it sounds pretty convincing, doesn't it?]
They grabbed the hapless bishop and dragged him into their temple, telling him he could either offer a sacrifice or be one. He replied that he couldn't respect a god that would be so troubled by a humble bishop living next door. So they dragged him back out and tied him to a bull which was then goaded into running rampant. The bull dragged Saturninus down a hill, bashing his skull open on a rock somewhere along the way. His body was hidden by a pair of faithful women until it became relics.
With so many pilgrims stopping in Toulouse on the Way of St. James, the fame of Saturninus spread far and wide. Many churches were dedicated to him, usually incorporating a bull into their iconography.