the Legion of Super Heroes' 30th century in New Earth. This world was used to allow crossovers with certain characters of the Legion of Super-Heroes and recreate characters that otherwise could not exist in the new continuity (such as Kryptonians, as in the New Earth Superman was the only survivor of Krypton). Alternate timelines were also used, the most notable event being Armageddon 2001 in 1991. An Antimatter Universe existed as well, which had some "reversed" events in a similar way as the former Earth-Three. The Earth within this Universe was called "Earth 2". In addition, there was a Limbo, where some heroes and characters that could not be brought back to "existence" after the Crisis on Infinite Earths lived outside the Universe. An important rule in the new DC Universe was that there could only be one timeline, so any change caused by time travelers caused the destruction of their timelines of origin. Changes in the past were often "fixed" or have to comply with the present to prevent continuity errors. Nevertheless, continuity errors appeared. The retold origin of Hawkman presented errors regarding the existence of the Golden Age version (Carter Hall) and the Silver Age version (Katar Hol) in the same continuity without a good explanation. The interaction of "possible timelines" also created continuity holes. This led to a new crisis to address the problem: the Zero Hour. The resulting universe had a slightly re-written story with no continuity errors even though it was acknowledged that reality-shattering events did happen (including the Crisis on Infinite Earths). This Universe kept the concept of one universe, one timeline. Such a timeline was "mapped" from the beginning to the present (1994) at the back cover of Zero Hour #0 that also included certain key dates in the future. The need to publish stories outside the strict DC Universe continuity led to the creation of certain DC imprints. Stories that set DC characters in different situations after the Crisis on Infinite Earths, were published by DC Comics under the Elseworlds imprint. None of these stories were ever intended to be included in the "real" continuity of the DC Universe. Certain characters were reinvented in a mature context and were published under the Vertigo imprint. Most of the times, the characters depicted within the Vertigo imprint had no relation to the original DC Universe's versions, nor did the events have influence over the