This ancient, extinct breed is named after the Molossi, tribespeople who inhabited the mountainous region in what is now north-west Greece, between the 5th and the 2nd centuries BC. It was primarily a guard dog, but also had other duties. In the past it has also been called the Molossan, the Molossian Hound or the Molosscicus and today it is sometimes referred to as the Molosser.
There are two conflicting opinions concerning this famous, ancient breed. The popular view is that it was the early forerunner of the mastiffs, and that it was the epitome of canine ferocity and aggression. Writing in the first century BC, the Roman poet and philosopher Lucretius vividly describes how `the angered Molossians' slack, wrinkled snouts lay bare in yawning jaws the threatening fence of fangs, in repressed snarl now raging their visceral fury'. This fearsome image is the one that has been handed down over the centuries. The general feeling is that some kind of gigantic guard dog was brought to Greece from a location lying to the east. There it became associated with the Molossi tribes and acquired their name.
Later, this impressive breed moved on towards Rome, where it was employed as the guard dog of the Roman army, accompanying the troops as they spread out across Europe. Wherever the armies went they left behind a few of their dogs and it was from these that most heavyweight breeds of Europe were descended. That view has been challenged by some authorities, who claim that it is based on guesswork and lacks detailed historical support. They point out that the pastoral Molossi tribes were regarded by the Greeks as backward barbarians living outside the enlightened Hellenic world, and were hardly likely to have developed a special breed of giant guard dogs. What they did have, apparently, was a more lightly built hunting dog that was swift, nimble, tall, with straight legs, a firm belly and soft ears that flowed back as it ran. This description of the Molossus dog, from the writings of Nemesianus in the 3rd century AD, sounds more like the big Greek Saluki than any kind of mastiff.
M. B. Wynn, in his classic 1886 work The History of the Mastiff, states categorically that the Molossus was not in reality a Mastiff.. the true Mollosian was an erect-eared, slate coloured or fawn, swift-footed wolfish-looking dog'. The best explanation of these contradictions seems to be that the Molossi had more than one type of dog.
It is worth remembering that Alexander the Great's mother was a Molossi princess and that Alexander, in the spectacular military wanderings that took him far to the east, is said to have encountered giant dogs which impressed him so much that he sent some home.
It would seem that, although the typical Molossus dogs may have been lighter, faster animals, some exceptional giant ones were also present in the 4th century BC, thanks to Alexander. It was these, presumably, that became the foundation stock for the mastiffs that were to follow. Whether we call Alexander's exotic, imported dogs by the name Molossus or not is largely a matter of taste. This is what has been done by most modern writers, who have chosen to ignore the native Molossian dog. It might be historically more accurate to call them something else, but that would only confuse matters. Source: Dogs - by Desmond Morris