The Levitation Act was a law passed throughout the Empire in 3E 421 which outlawed the use of levitation magic. Because the Imperial governed province of Morrowind retained self-rule and house traditions under the Treaty of the Armistice, it was not subject to the ban. As such, levitation magic was still prevalent in Morrowind up until at least the late Third Era—most notably by Telvanni wizards, whose towers required the knowledge of levitation magic in order to reach the upper levels. Although levitation was banned in some parts of the province, namely in Mournhold, by the will of Almalexia herself.
Due to the ban, the knowledge of levitation magic was largely lost by 4E 40, and almost unheard of for many years prior. Some individuals retained what knowledge there was, including a Synod mage named Lazarum, who apparently knew of a levitation spell. A potion brewed with the ichor of a Winged Twilight was supposedly used by two individuals to travel to the floating city of Umbriel. Some Telvanni towers, such as Tel Mithryn on Solstheim, had magical runes fitted at the base of the stem which granted anyone access, however it is unknown if this was related to the Levitation Act.
Dovyn Aren, a well known teacher of levitation magic prior to the Levitation Act
The Telvanni tower of Tel Naga, as seen in Morrowind