English: Detail view of the Fitzcarrald Ishtmus (Istmo Fitzcarral a.k.a. Istmo Fitz-Carrall) as mapped in 1904 by Rafael E. Baluarte. The Ishtmus, discovered by Carlos Fermin Fitzcarrald, is a land bridge that is the shortest connection between the Serhali river (a tributary of the Urubamba and Amazon rivers) as well as the Caspajhali river, a tributary of the Madre de Dios river. The significance of this land bridge is that it connected Iquitos and Puerto Maldonado (and in extension, Bolivia) for the rubber trade in the early 20th century, a significant discovery for the rubber trade.