The Great St Bernard Pass is a high mountain road through the Alps between Switzerland and Italy. Long ago, travellers crossing it in winter often got caught by sudden snowstorms. At the very top of the pass, a group of helpful monks ran a shelter for these travellers. Around 350 years ago, they began breeding big, strong dogs to help find anyone lost in the snow.
The dogs were perfect for the job. Their huge size meant they could push through deep snow. Their thick coats kept them warm. Their amazing sense of smell could detect a human buried under metres of snow. They worked in pairs or threes - one dog would stay with the lost traveller to keep them warm while the others went to fetch help.
The most famous Saint Bernard was a dog called Barry, who lived around 200 years ago. People say Barry helped rescue more than 40 lost travellers in the snow during his lifetime. Today his stuffed body is on display in a natural history museum in Bern.
Most Saint Bernards now live as gentle family dogs. They are famously calm and patient, which is why they are often shown in cartoons looking after children. The Swiss army still keeps a few Saint Bernards at the original mountain pass, but rescues are now done by helicopter.