Many centuries passed before any real improvement was made upon the old Egyptian plow. If there were any improvement anywhere it was among the Romans. We read in Pliny--a Roman writer of the first century--of a plow that had wheels to regulate the depth of the plow and also a _coulter_, that is, a knife fixed in front of the share to make the first cut of the sod (Fig. 6). But such a plow was not in general use in Pliny's time. A thousand years later, however, the plow with wheels and coulter was doubtless in common use. In a picture taken from an old Saxon print we see (Fig. 7) a plow which was used in the time of William the Conqueror (1066). Here the plow has a coulter inserted in the beam and there are two wheels to regulate the depth to which the plow may go. This Saxon plow is drawn by four fine oxen and it is plainly a great improvement upon the old Egyptian plow. [Illustration: FIG. 6.--PLINY'S PLOW, 70 A. D.] [Illustration: FIG. 7.--AN OLD SAXON PLOW, 1000 A. D.] [Illustration: FIG. 8.--A DOUBLE PLOW OF THE SEVENTEENTH CENTURY. (This plow was proposed but was never made.)] But improvements in the plow during the dark ages came very slowly. At the time of the discovery of America the plow was still the clumsy wooden thing it was five hundred years before. In the sixteenth and seventeenth centuries, however, when improvements were being made in so many things, it was natural that men should begin to think of trying to improve the plow. In an old book published in 1652 we read of a double plow--one which would plow two furrows at one time. A picture (Fig. 8) of the double plow is given in the book but there is no proof that such a plow was ever made or ever used. The world did not as yet need a double plow, although the time was to come when it would need one. In the early part of the eighteenth century we begin to see real improvements in plow making. About this time Dutch plowmakers began to put _mold-boards_ on their plows. The purpose of the mold-board is to lift up and turn over the slice of sod cut by the share. Without the mold-board the plow simply runs through the ground and stirs it up. With the mold-board of the Dutch plow (Fig. 9) the sod was turned completely over and the weeds and grass were covered up. This was the kind of plow that was needed, for if the weeds and grass are not covered up the best effects of plowing are lost. So the mold-board was a great improvement and its invention marks a great event in the history of the plow. [Illustration: FIG. 9.--THE DUTCH PLOW SHOWING THE MOLD-BOARD.]