Standing about 1.8 metres at the shoulder, with large horns, and weighing in at somewhere around 3,000 lbs.
In February of 1999, archaeologists in Britain found the almost complete remains of Bovis Primigenius, the wild aurochs, dating to about 2500 B.C. It had been ceremonially buried, with the flint arrow-heads used to hunt it left inside the body. The skull was almost completely intact, including the almost metre-long, lyre-shaped horns, missing only a small portion of the back.
This buried beast was probably among the last of its kind on the island; by the Bronze Age, the aurochs was almost completely gone from the British Isles, hunted to extinction for its horns, skin, meat, and bones, every part useful for a growing civilisation.
That left only the continent, particularly the dark forests of Germania, in what would later become Prussia, Lithuania, and Poland. Early palaeolithic paintings depict these great beasts being hunted. Julius Caesar in his De Bello Gallico talks about the wild cattle of the Gallic and German forests, and Tacitus in his Annales notes the difference between the thickness of the hides of the domestic cattle and wild aurochs.
The systematic hunting of the Aurochs led to their gradual extinction; the hunt was generally conducted by driving the lone cow into the waiting nets and spears of a sometimes mounted ambush, where the waiting "hunters" pretty much planted their spears in the ground and waited for the rampant cow to run into them, or at least hoped to spear it while it gored somebody else. Already in the 13th century, the herds were pretty scarce; a few hunts are mentioned in the chronicles of the Teutonic Knights in the late 14th century. In Poland in the 15th century, the only surviving aurochs were kept on royal or noble game preserves. The last aurochs cow died in 1627, of natural causes, on the hunting grounds of King Jactorow in Masovia, who made a concerted effort not to kill it (it probably just died before he had the chance).
Recently, a German zoologist has attempted to resurrect the aurochs by cross-breeding several species of British and Spanish cattle; the result seems to be a somewhat accurate but rather pale specimen of the greatest, most feared cow in history.