Louisville was founded in 1779 at the only major natural navigational barrier on the river, the Falls of the Ohio. The Falls were a series of rapids where the river dropped in a stretch of about . In this area, the river flowed over hard, fossil-rich beds of limestone. The first locks on the river the Louisville and Portland Canal were built between 1825 and 1830 to circumnavigate the falls. Fears that Louisville's transshipment industry would collapse proved ill-founded: but the increasing size of steamships and barges on the river meant that the outdated locks could serve only the smallest vessels until well after the Civil War when improvements were made. The U.S. Army Corps of Engineers improvements were expanded again in the 1960s, forming the present-day McAlpine Locks and Dam.