Answer based on context:

Between 1714-20, several Russian sailors had mapped the Caspian Sea. On 15 July 1722, Peter issued a manifesto in several local languages justifying the invasion, drawn up by Dimitrie Cantemir. Peter gathered 22,000 infantry, 9,000 dragoons and 70,000 Cossacks, Tatars and Kalmyks. For transport, he created the Caspian Flotilla at Astrakhan under Fyodor Apraksin. The infantry, artillery and stores were to be shipped by sea to the mouth of the Sulak River while the cavalry went overland from Tsaritsyn and Mozdok. By the time Peter was assembling his forces for the attack, the Safavid state had already entered the final stages of collapse.

How many years time span did several Russian Sailors map the Caspian Sea?
6