Marinus' geographical treatise is lost and known only from Ptolemy's remarks. He introduced improvements to the construction of maps and developed a system of
nautical charts. His chief legacy is that he was the first to assign to each place a proper
latitude and
longitude. His
zero meridian ran through the westernmost land known during his time, the
Isles of the Blessed, around the location of the present-day
Canary or
Cape Verde Islands. He used the parallel of
Rhodes for measurements of latitude. Ptolemy mentions several revisions of Marinus' geographical work, which is often dated to AD 114, although this is uncertain. Marinus estimated a length of 180,000
stadia for the equator, roughly corresponding to a
circumference of the Earth of , about 17% less than the actual value. Marinus also carefully studied the works of his predecessors and the diaries of travelers. His maps were the first in the Roman Empire to show China. He invented
equirectangular projection, which is still used in map creation today. A few of Marinus' opinions are also reported by Ptolemy. Marinus was of the opinion that the
World Ocean was separated into an eastern and a western part by the continents of Europe, Asia and Africa. He thought that the inhabited world stretched in latitude from
Thule (Norway) to
Agisymba (around the
Tropic of Capricorn) and in longitude from the
Isles of the Blessed (around the
Canaries) to
Sera (China). Marinus also coined the term
Antarctic, referring to the opposite of the
Arctic. In 1935, an
impact crater on the Moon was named after Marinus. ==See also==