The name "Ohio" comes from the Seneca, , lit. "Good River". European discovery of the Ohio River may be attributed to English explorers from Virginia in the latter half of the 17th century. In his "Notes on the State of Virginia" published in 1781–82, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted." In the late 18th century, the river was the southern boundary of the Northwest Territory. It became a primary transportation route for pioneers during the westward expansion of the early U.S.