But the disadvantages of the system are obvious, for an event might appear of great importance in one city and might be of no interest to another situated at some distance from it. Thus it happened that the same event was not employed throughout the whole country for designating a particular year, and we have evidence that different systems of dating were employed in different cities. Moreover, it would have required an unusually good memory to fix the exact period of a document by a single reference to an event which took place in the year when it was drawn up, more especially after the system had been in use for a considerable time. Thus, in order to fix the relative dates of documents without delay, the scribes compiled lists of the titles of the years, arranged in order under the reigns of the successive kings, and these were doubtless stored in some archive-chamber, where they were easily accessible in the case of any dispute arising with regard to the date of a particular year. It is fortunate that some of these early Sumerian date-lists have been recovered, and we are furnished by them with an outline of Sumerian history, which has the value of a contemporary record.[2] They have thrown light upon a period of which at one time we knew little, and they have served to remove more than one erroneous supposition. Thus the so-called Second Dynasty of Ur was proved by them to have been non-existent, and the consequent reduplication of kings bearing the names of Ur-Engur and Dungi was shown to have had no foundation in fact.