Abramo Ortellio.

A turning-point in his career was reached in 1564 with the publication of a World Map in eight sheets of which only one copy is known: other individual maps followed and then - at the suggestion of a friend - he gathered together a collection of maps from contacts among European cartographers and had them engraved in uniform size and issued in 1570 as the Theatrum Orbis Terrarum (Atlas of the Whole World). Although Lafreri and others in Italy had published collections of 'modern' maps in book form in earlier years, the Theatrum was the first uniformly sized, systematic collection of maps and hence can be called the first atlas, although that term itself was not used until twenty years later by Mercator.

The Theatrum, with most of its maps elegantly engraved by Frans Hogenberg, was an instant success and appeared in numerous editions in different languages including addenda issued from time to time incorporating the latest contemporary knowledge and discoveries. The final edition appeared in 1612. Unlike many of his contemporaries Ortelius noted his sources of information and in the first edition acknowledgement was made to eighty-seven different cartographers.

Apart from the modern maps in his major atlas, Ortelius himself compiled a series of historical maps known as the Parergon Theatri which appeared from 1579 onwards, sometimes as a separate publication and sometimes incorporated in the Theatrum.