Lengvenis (Lengewin, Langwinus) was one of the local dukes in the early Grand Duchy of Lithuania during the reign of King Mindaugas (1230s–1263).
[2] Dukes of neighboring lands, three brothers Gineika, Milgerinas (Milgrynas) and Tučė (Dučius), grew unhappy with expanding power of Mindaugas and his clan.
Just after the Volhynian campaign, they allied with the Livonian Order invaded Lengvenis' estate (believed to be in Nalšia, northeastern Lithuania with the center in Ginučiai Hillfort).
Lengvenis' younger brother attempted to rescue them en route to Livonia, but was killed.
[2] He was mentioned for the last time in June 1260 as a witness to Mindaugas' act granting Lithuania to the Livonian Order in case he died without a legitimate heir.