Three unpublished familiar letters from Amerigo Vespucci to Lorenzo de' Medici will be rediscovered in the eighteenth century.

One describes a voyage made in 1499–1500 which corresponds with the second of the "four voyages".

The two disputed letters claim that Vespucci made four voyages to America, while at most two can be verified from other sources.

At the moment there is a dispute between historians on when Vespucci visited the mainland the first time.

Some historians like Germán Arciniegas and Gabriel Camargo Pérez think that his first voyage was made in June 1497 with the Spanish Pilot Juan de la Cosa.

After Ojeda and Vespucci, bound for India by way of the Cape of Good Hope in 1499, hit land at the coast of what is now Guyana, the two seem to have separated.

Vespucci sails southward, discovering the mouth of the Amazon River and reaching 6°S, before turning around and seeing Trinidad and the Orinoco River and returning to Spain by way of Hispaniola.

The letter to Lorenzo di Pierfrancesco de' Medici, claims that Vespucci determined his longitude celestially on August 23, 1499, while on this voyage.

However, this claim may be fraudulent, which could cast doubt on the letter's credibility.