The assertion of Tacitus, that Germany was destitute of the precious metals, must be taken, even in his own time, with some limitation (Germania, chapter 5, Annals xi. 20). According to Spener (Hist. Germaniae Pragmatica, tom. i. p. 351),
Argentifodinae in Hercyniis montibus, imperante Othone magno (A.D. 968) primum apertae, largam etiam opes augendi dederunt copiam:
but Rimius (p. 258, 259) defers till the year 1016 the discovery of the silver mines of Grubenhagen, or the Upper Hartz, which were productive in the beginning of the 14th century, and which still yield a considerable revenue to the house of Brunswick.