Some of the earliest human art to survive consists of engraved or painted works on open-air rocks or on the floors, walls, and ceilings of caves, some of them in deep crannies. They were created during the Upper Paleolithic period (40,000 to 10,000 B.C.), and the best were done by what we call the Magdalenians (from the name of a site), peoples who flourished in Europe from 18,000 to 10,000 B.C. Such works have a unity and can be described as the Magdalenian art system, the first in human history. It was also the longest, lasting for much of the total time humans have produced art. In any history of art, then, the Magdalenian system must occupy a place of importance. Also, of all the forms of art practiced on the planet, it is the one about which we know the least. But we do possess a reasonable amount of knowledge, bearing in mind that the first cave art was only discovered in the 1860s, and it was not until 1902 that it was accepted as a fact by anthropologists and art historians. By the end of the twentieth century, there were 277 agreed examples in Europe. Unfortunately, most cave art works are extremely fragile. When a cave is opened and the conditions that enable the paintings to survive are altered, deterioration can be rapid. Thus except in places where expensive air-conditioning has been installed, caves are no longer open to the public. Even the Altamira cave in Spain, finest of them all, is now open only to small parties for brief periods. Scholars themselves find it difficult to gain admission. Some of these works are photographed, but the camera gives a poor idea of their nature and quality. Some are difficult to see anyway: the best part of Altamira has to be studied lying down. Hence inaccessibility is a real and growing obstacle to unlocking the secrets of the Magdalenian art system. However, there is some knowledge on which we can build, beginning with subject matter. Cave art portrays human hands, large numbers of animals in different activities, including various species, such as the woolly rhinoceros, that are now extinct and a few that were extinct even at the time they were painted, geometric figures, and signs. Humans are also portrayed, but these instances are rare. Next we come to methods and materials. The earliest and most rudimentary images are finger drawings in soft clay on the rock surface, the artist following the example of claw marks made by animals. Then came engraving (using a tool to cut into a material), by far the commonest method, using flakes of sharp flint and in some cases stone picks. Different types of rock, and rock formations, were used to give variety, add color, and produce depth, so that some of these engravings are akin to sculptural low reliefs (shallow sculptures carved into walls). Fine engraving is rare and late. Clay engraving on the floors has been obliterated by the feet of modem visitors, but some good examples survive. Finally, and most impressively, we get painting. The first colors were red, iron oxide (hematite, a form of red ochre), and black (manganese dioxide), though black from juniper or pine carbons has also been discovered. White from kaolin or mica was used occasionally. The only other colors available to Magdalenian painters were yellow and brown. However, great ingenuity was displayed by artists. At Lascaux cave we have found pestles and mortars in which colors were mixed, together with no less than 158 different mineral fragments from which the mixtures were made. There seems to have been no shortage of pigment – large lumps have been found at some sites. Shells of barnacles were used as containers. One artist employed a human skull. Cave water and the calcium it contained were used as mixers, and vegetable and animal oils as binders. The artists had primitive crayons, and they applied the paint with brush tools, though none have survived. All kinds of devices and implements were used to aid art. Important lines were preceded by dots, which were then joined up. Sometimes paint was sprayed. Stencils were used. Blowpipes made from bird bones served as tubes for applying paint. By these means, Magdalenian painters were able to produce polychrome art.