Illustrated Companion to the Latin Dictionary/Mutationes

This article incorporates text from a publication now in the public domain: Rich, Anthony (1849). The illustrated companion to the Latin dictionary, and Greek lexicon. p. vi. OCLC 894670115. https://archive.org/details/illustratedcompa00rich. 

MUTATIO'NES. Posting-houses, at which relays of horses were kept along the high roads for the service of the state, and the accommodation of travellers. The postmaster of the smallest mutatio was compelled to keep as many as twenty horses; of the largest, not less than forty. Impp. Arcad. et Honor. Cod. Theodos. 8. 5. 53. Cod. Just. 12. 51. 15. Compare Ammian. xi. 9. 4., where the word is used for a relay or change of horses.