As we picture the prosperity of those medieval days there comes into our minds that winding silver stream which made such prosperity possible, and we seem to see the River Thames crowded with ships from foreign parts, many of them bringing wine from France, Spain, and other lands, for wine was one of the principal imports of the Middle Ages, and filling up the great holds of their empty vessels with England’s superior wool; others from Italy, laden with fine weapons and jewels, with spices, drugs, and silks, and all wanting our wool. A few of those ships in the Pool were laden with _coal_, for in the Middle Ages this new fuel—sea-coal, as it was called to distinguish it from the ordinary wood charcoal—made its appearance in London. Nor did London take to it at first. In the reign of Edward I. the citizens sent a petition, praying the King to forbid the use of this “nuisance which corrupteth the air with its stink and smoke, to the great detriment of the health of the people.” But the advantages of the sea-coal rapidly outweighed the disadvantages with the citizens, and the various proclamations issued by sovereigns came to nought. Before long several officials were appointed to act as inspectors of the new article of commerce as it came into the wharves. The famous Dick Whittington and various other prominent citizens of London made large fortunes from their coal-boats. CHAPTER SEVEN _The Tower of London_ London has many treasures to show us, if we take the trouble to look for them, but it has no relic of the past so perfect as its Tower—a place which every Briton, especially every Londoner, ought to see and try to understand. If only the Tower’s silent old stones could suddenly gain the power of speech, what strange tales they would have to tell of the things which have occurred during their centuries of history—tales of things glorious and tales of things unspeakably tragic. Though the latter would easily outweigh the former in number, I am afraid; for this grim stronghold is a monument to evil rather than to good. The Tower has often been spoken of as the _key_ to London, and there is truth in the saying, for its position is certainly an excellent one. When William of Normandy descended on England with his great company of knights and their retainers, he professed to have every consideration for the people of London, and certainly he treated the citizens quite fairly according to the terms of the treaty. But, at the same time, he apparently did not feel any too sure of them, and so he called in the monk, Gundulf, to erect a fortress, which to all appearances was merely a strengthening of the fortifications already there, but which in reality was intended to serve as a constant reminder of the power and authority of the conquering king.