Sirius was sometimes confused with another two-headed beast called Orthrus. This was Geryon's watchdog; his job was to guard the tyrant's cattle. Hercules captured the cattle (as his Tenth Labor), killing Orthrus in the process.
Canis Major, the largest of Orion's two hunting dogs, might be chasing Lepus, the Rabbit, who is just in front of him. Or perhaps he is ready to help Orion battle the great bull.
The Romans associated other nearby stars with Sirius and pictured it as a dog.
The Arabic title for the constellation was Al Kalb al Jabbar, or "the Dog of the Giant."
The ancient Egyptians believed that the flooding of the River Nile was caused by the "power" of the star Sirius. The Egyptian records show that the rising of Sirius at dawn was used by the astronomer-priests at least as early as 3000 B.C. The day on which Sirius was first seen to rise at dawn became New Year's Day for the Egyptians, and they called Sirius "Mistress of the Year." In honor of Sirius, the Egyptians oriented temples so that they faced that point on the horizon where Sirius was first seen to rise at dawn. One such temple was built as early as 2700 B.C.
The stories concerning Orion's dogs are not of mythic proportion, but the Greeks did have several interesting beliefs concerning Sirius. The Athenian New Year began with the appearance of Sirius. He was seen as two-headed, like the Roman God Janus: looking back at the past year and forward to the new one.
In antiquity, as Homer and Hesiod were writing their stories, the Dog Star was already associated with the Sun, since the Sun enters that part of the sky in the hot summer months. The ancients thought that the heat of Sirius was added to that of the Sun. To this day we call the hottest portion of summer the "dog days."
The name Sirius may come from the Greek meaning "scorching." Now days the star is mostly thought of as a winter star, accompanying Orion, rather than as the summer home of the sun.
According to the Polynesians, Sirius was not always the brightest star. They believed that the Pleiades were much brighter than Sirius. The Pleiades had a reputation of bragging about their beauty. One day Sirius convinced the god Tane to hurl the star Aldebaran at this brightest star, shattering it into the group of six stars we see now.