Johannes Grant or Johannis Grandi was a mercenary employed by the Byzantine Empire at the fall of Constantinople in 1453. Contemporary Greek and Latin accounts referred to him as being German, although Runciman has suggested he may actually have been a Scot named John Grant. He appears to have been affiliated with the Genoese contingent of mercenaries at the siege, possibly part of the men commanded by Giovanni Giustiniani. His use of counter-mining tunnels prevented the Turks from weakening or invading Constantinople from under the walls. He would fill barrels with water and observe the waves, using incendiary weapons, mostly Cheirosiphon to destroy Ottoman tunnels. 
Depictions in Fiction
- Grant appears as a minor character in The Dark Angel by Mika Waltari
- John Le Grant, an Aberdonian based on the historical Johannes Grant, appears in The House of Niccolò by Dorothy Dunnett
- John Grant is the central character in the historical novel Porphyry and Ash
- John Grant is featured in the third episode of the historical docudrama series Rise of Empires: Ottoman; here he is depicted as Scottish.
- John Grant is the central character in the historical novel Master of Shadows by Neil Oliver
- In the EU4 mod The Third Odyssey (an Alternate history scenario in which the Byzantines flee to America before the fall of Constantinople) Johannes Grandt is an Austrian advisor who rediscovers the secret to Greek fire.
- Leonard of Chios: "Johannis Grandi Alemani", where Grandi can also mean "the great" in Italian
- Georgios Sphrantzes: "Johannes the German"
- Bartusis, Mark, Late Byzantine Army
- Runciman, Steven, Fall of Constantinople 1453, page 84
- Nicol, Donald, Last Centuries of Byzantium. Cambridge University Press, 1993 [2nd edition]. Chapter 18.
- The Fall of Constantinopla Archived 6 February 2007 at the Wayback Machine