_Tacitus_,[333] in the same way (A.D. _circa_ 90), speaks of the soil of Britain as fertile and bearing heavy crops (_patiens frugum_), and describes the tricks of the tax gatherers in collecting the _tributum_, which was exacted in corn.[334] «Strabo.» _Strabo_[335] (B.C. 30) mentions the export from Britain of '_corn_, cattle, gold, silver, iron, skins, slaves, and dogs.' «Diodorus Siculus.» _Diodorus Siculus_[336] (B.C. 44) describes the manner of reaping and storing corn in England thus:-- They have mean habitations constructed for the most part of reeds or of wood, and they gather in the harvest by cutting off the ears of corn and storing them in subterraneous repositories; they cull therefrom daily such as are old, and dressing them, have thence their sustenance. . . . The island is thickly inhabited. «Pytheas.» Lastly, we have been recently reminded by Mr. Elton that _Pytheas_, 'the Humboldt of antiquity,' who visited Britain in the fourth century B.C., saw in the southern districts abundance of wheat in the fields, [p249] and observed the necessity of threshing it out in covered barns, instead of using the unroofed threshing-floors to which he was accustomed in Marseilles. 'The natives,' he says, 'collect the sheaves in great barns, and thresh out the corn there, because they have so little sunshine that our open threshing-places would be of little use in that land of clouds and rain.'[337] It is clear, then, that in the south-east of Britain a considerable quantity of corn was grown all through the period of Roman rule and centuries before the Roman conquest of the island. And if so, that difference between the pastoral tribal districts of the interior and the more settled agricultural districts of the south and east, noticed by Cæsar, was one of long standing. The tribal system of Wales furnishes us, therefore, with no direct key to the economic condition of South-eastern Britain. But, on the other hand, the continuous and long-continued growth of corn in Britain from century to century adds great interest to the further question, Upon what system was it grown? «The corn probably grown on the open-field system.»