雷蒂亚（拉丁语：Raetia，或作Rhaetia），是罗马帝国建于公元15年的行省，名字来源于拉埃提亚人（Raeti）。其土地相当于今瑞士东、中部（包括莱茵河上游和博登湖），巴伐利亚南部，上施瓦本，福拉尔贝格州，蒂罗尔大部及一部分伦巴第。前16年，罗马帝国出兵入侵阿尔卑斯山东部和多瑙河上游地区，创建了雷蒂亚和诺里库姆两个行省。南方即意大利本土，东南为诺里库姆，西为上日耳曼尼亚。

意大利为一个特别的行政单位，从未被立为罗马行省

Raetia (/ˈriːʃə/ or /ˈriːʃiə/, Latin: [rajtia], also spelled Rhaetia) was a province of the Roman Empire, named after the Rhaetian (Raeti or Rhaeti) people. It bordered on the west with the country of the Helvetii, on the east with Noricum, on the north with Vindelicia, on the west with Transalpine Gaul and on south with Venetia et Histria. It thus comprised the districts occupied in modern times by eastern and central Switzerland (containing the Upper Rhine and Lake Constance), southern Bavaria and the Upper Swabia, Vorarlberg, the greater part of Tirol, and part of Lombardy. Later Vindelicia (today south-eastern Wuerttemberg and south-western Bavaria) formed part of Raetia. The northern border of Raetia during the times of Augustus and Tiberius was the River Danube. Later the Limes Germanicus marked the northern boundary, stretching for 166 km north of the Danube. Raetia linked to Italy across the Alps over the Reschen Pass, by the Via Claudia Augusta. The Romansh people living in Southeast Switzerland are believed to be direct descendants of the Raetians. However, the exact lineage of the Romansh (or Romansch) people remains incomplete.