Owing to financial difficulties the payments to von Taxis from the royal exchequer could not be kept up, and in order to maintain the service another source of revenue had to be discovered. It was found in the acceptance for transmission by the posts of private letters, and in allowing the use of the posts by private persons desirous of travelling. This was made part of the ordinary business of the posts, with the reservation that the use of the posts by private persons should not interfere with or impede the official service.[712] In 1512 the Emperor Maximilian conferred on Francis von Taxis, and on several others of his family, titles of hereditary nobility in the Empire and in the Austrian and Burgundian dominions, together with the dignity of Count Palsgrave.[713] In 1516 the Taxis posts were extended to Verona, Rome, and Naples, and were improved and accelerated. In 1615 the office of Imperial Postmaster-General was conferred on Lamoral von Taxis and his descendants as an hereditary fief. The actual development of the posts was of a twofold character. At first the Taxis family were able to establish their posts in various parts of the Empire without opposition; the princes were themselves satisfied with their messenger systems, and were indisposed to establish posts on account of the heavy cost. But after a time, when the profitable character of the Taxis posts became apparent,[714] the princes questioned the right of the Imperial Postmaster-General to lay posts within their territories, and claimed that they alone possessed that right.[715] In 1597 the posts were proclaimed an Imperial reservation,[716] but this theory was never accepted by the princes.[717] The Taxis posts, therefore, never became general throughout the Empire. Eights were obtained in certain States, so that they became an important system reaching many parts of the Empire; but they did not altogether supplant the territorial services.[718]