Having returned from the north of the Thames, Pytheas crossed the North Sea to the mouth of the Rhine, a passage which took about two and a half days. He gives a pitiable account of the people living on the Dutch coast and their perpetual struggle with the sea. The natives had not learnt the art of making dykes and embankments. A high tide with a wind setting toward the shore would sweep over the low-lying country and swamp their homes. A mounted horseman could barely gallop from the rush and force of these strong North Sea tides. But the Greek geographers would not believe this; they only knew the tideless Mediterranean, and they thought Pytheas was lying when he told of the fierce northern sea. Pytheas sailed past the mouth of the Elbe, noting the amber cast upon the shore by the high spring tides. But all these interesting discoveries paled before the famous land of Thule, six days' voyage north of Britain, in the neighbourhood of the frozen ocean. Grand excitement reigned among geographers when they heard of Thule, and a very sea of romance rose up around the name. Had Pytheas indeed found the end of the world? Was it an island? Was it mainland? In the childhood of the world, when so little was known and so much imagined, men's minds caught at the name of Thule--Ultima Thule--far-away Thule, and weaved round it many and beautiful legends. But to-day we ask: Was it Iceland? Was it Lapland? Was it one of the Shetland Isles? [Illustration: NORTH BRITAIN AND THE ISLAND OF THULE. From Mercator's edition of Ptolemy's map.] "Pytheas said that the farthest parts of the world are those which lie about Thule, the northernmost of the Britannic Isles, but he never said whether Thule was an island or whether the world was habitable by man as far as that point. I should think myself"--the speaker is Strabo, a famous Greek traveller who wrote seventeen books of geography--"I should think myself that the northern limit of habitude lies much farther to the south, for the writers of our age say nothing of any place beyond Ireland, which is situate in front of the northern parts of Britain." Pytheas said that Thule was six days' sail north of Britain. "But who in his senses would believe this?" cries Strabo again. "For Pytheas, who described Thule, has been shown to be the falsest of men. A traveller, starting from the middle of Britain and going five hundred miles to the north, would come to a country somewhere about Ireland, where living would be barely possible."