Complex sentence: In Leuven, he worked with Gemma Frisius and Gaspar Myrica from 1535 to 1536 to construct a terrestrial globe, although the role of Mercator in the project was not primarily as a cartographer, but rather as a highly skilled engraver of brass plates.
Split into simpler sentences: In Leuven, he worked with Gemma Frisius and Gaspar Myrica from 1535 to 1536 to construct a terrestrial globe. Although the role of Mercator in the project was not primarily as a cartographer, but rather as a highly skilled engraver of brass plates.