"Here be dragons" means dangerous or unexplored territories, in imitation of a medieval practice of putting illustrations of dragons, sea monsters and other mythological creatures on uncharted areas of maps where potential dangers were thought to exist.
History
Although several early maps, such as the Theatrum Orbis Terrarum, have illustrations of mythological creatures for decoration, the phrase itself is an anachronism. The only known historical use of this phrase is in the Latin form "HC SVNT DRACONES" on the Hunt-Lenox Globe. Earlier maps contain a variety of references to mythical and real creatures, but the Lenox Globe is the only known surviving map to bear this phrase. The term appeared on the Lenox Globe around the east coast of Asia, and might be related to the Komodo dragons in the Indonesian islands, tales of which were quite common throughout East Asia. The classical phrase used by ancient Roman and Medieval cartographers was HIC SVNT LEONES when denoting unknown territories on maps.
The Borgia map, in the Vatican Library, states, over a dragon-like figure in Asia, "Hic etiam homines magna cornua habentes longitudine quatuor pedum, et sunt etiam serpentes tante magnitudinis, ut unum bovem comedant integrum.".
The Fra Mauro Map has the "Island of Dragons", an imaginary island in the Atlantic Ocean. In an inscription near Herat, Fra Mauro says that in the mountains nearby "there are a number of dragons, in whose forehead is a stone that cures many infirmities", and describes the locals' way of hunting those dragons to get the stones. This is thought to be based on Albertus Magnus's treatise De mineralibus. In an inscription elsewhere on the map, the cartographer expresses his skepticism regarding "serpents, dragons and basilisks" mentioned by "some historiographers".
A 19th-century Japanese map, the :File:Jishinnoben1855.jpg|Jishin-no-ben, in the shape of ouroboros, depicts a dragon associated with causing earthquakes.
Ptolemy's atlas in Geographia warns of elephants, hippos and cannibals.
Tabula Peutingeriana has "in his locis elephanti nascuntur", "in his locis scorpiones nascuntur" and "hic cenocephali nascuntur".
Cotton MS. Tiberius B.V. fol. 58v, British Library Manuscript Collection, has "hic abundant leones", along with a picture of a lion, near the east coast of Asia ; this map also has a text-only serpent reference in southernmost Africa : "Zugis regio ipsa est et Affrica. est enim fertilis. sed ulterior bestiis et serpentibus plena"
The Ebstorf map has a dragon in the extreme south-eastern part of Africa, together with an asp and a basilisk.
Giovanni Leardo's map has, in southernmost Africa, "Dixerto dexabitado p. chaldo e p. serpent".
Martin Waldseemüller's Carta marina navigatoria has "an elephant-like creature in northernmost Norway, accompanied by a legend explaining that this 'morsus' with two long and quadrangular teeth congregated there", i.e. a walrus, which would have seemed monstrous at the time.
Waldseemüller's Carta marina navigatoria, revised by Laurentius Fries, has the morsus moved to the Davis Strait.
Bishop Olaus Magnus's Carta Marina map of Scandinavia has many monsters in the northern sea, as well as a winged, bipedal, predatory land animal resembling a dragon in northern Lapland.
On the maps surrounding imperialism, up until the Berlin Conference of 1885 and the discoveries made by Livingstone, elephants were drawn in as is shown by this excerpt from "On Poetry: a Rhapsody" by Jonathan Swift: "So geographers, in Afric maps, With savage pictures fill their gaps, And o'er uninhabitable downs, Place elephants for want of towns."
