Care was also taken at once that he should be able to correspond at least by letter with his friends, and especially with those at Wittenberg. These letters were sent by messengers of the Elector through the hands of Spalatin. When Luther afterwards heard that a rumour had got abroad as to his place of residence, he sent a letter to Spalatin, in which he said: 'A report, so I hear, is spread that Luther is staying at the Wartburg near Eisenach; the people suppose this to be the case, because I was taken prisoner in the wood below; but while they believe that, I sit here safely hidden. If the books that I publish betray me, then I shall change my abode; it is very strange that nobody thinks of Bohemia.' This letter, so Luther thought, Spalatin might let fall into the hands of some of his spying opponents, so as to lead them astray in their conjecture. Spalatin made no use of this naive attempt at trickery. He could hardly have done much in the matter, and would probably have directed those who saw through the meaning of the letter straight to the Wartburg. He succeeded, however, remarkably well in keeping the spot a secret, even after it was generally guessed and known that Luther was to be found somewhere in Saxony. As late as 1528, Luther's friend Agricola remarks that he had hitherto remained concealed, whilst some even sought to hear of him by questioning of the devil; and more than twenty years later Luther's opponent Cochlaeus declares that he was hidden at Alstedt in Thuringia. There was no imperial power at that time which might have deemed it necessary or expedient to track out the man who had been condemned by the Edict of Worms. The Emperor had left Germany again, and was engaged in a war with France. In his quiet solitude Luther threw himself again without delay into the work of his calling, so far as he could here perform it. This was the study of Scripture and the active exercise of his own pen in the service of God's Word. He had now more time than before to investigate the meaning of the Bible in its original languages. 'I sit here,' he writes to Spalatin ten days after his arrival, 'the whole day at leisure, and read the Greek and Hebrew Bible.' His sojourn at the castle began in the festival time between Easter and Whitsuntide. He wrote at once an exposition of the sixty-eighth Psalm, with particular reference to the events of Ascension and Whitsuntide.