The Molossus (Greek: Μολοσσός, romanized: Molossós), also known as the Molossian hound and Epirus mastiff, is an extinct dog breed from Ancient Greece.

[1][2] The Molossus were famous throughout the ancient world for their size and ferocity and were frequently mentioned in ancient literature, including the writings of Aristophanes,[3] Aristotle,[4] Grattius,[5] Horace,[6][7] Lucan,[8] Lucretius,[9] Martial,[10] Nemesianus,[11] Oppian of Apamea,[12] Plautus,[13] Seneca,[14] Statius,[15][16][17] Ovid,[18] and Virgil.

[1] It is sometimes stated in books and magazines, particularly in Continental Europe and North America, that all mastiff-type dogs are descended from the Molossus.

[2] This theory has been questioned by many experts who state it relies on guesswork and lacks historical evidence, and that mastiffs likely developed elsewhere.

[21] A number of modern kennel clubs, including the Fédération Cynologique Internationale, group the distinct mastiffs with livestock guardian dogs as a single type they call "molossoid".