In the 1990s, Richard Serra's art underwent significant evolution, reflecting both a deepening of his sculptural practice and a broadening of his conceptual horizons. During this decade, Serra continued to explore the possibilities of Corten steel, creating monumental sculptures that engaged with their environments in complex ways. His works from this period are characterized by their massive scale, simple yet powerful forms, and the way they shape the viewer's experience of space and movement. One of the most notable developments in Serra's work during the 1990s was the introduction of the "Torqued Ellipse" series. These sculptures, with their twisting and bending forms, marked a departure from the more straightforward geometric shapes that had characterized his earlier work. The "Torqued Ellipses" invite viewers to move around and through them, creating a dynamic interaction between the sculpture, the site, and the viewer. The experience of these works is often described in terms of the sublime, evoking feelings of awe, disorientation, and a heightened awareness of one's own physicality and perception​ (Artnet News)​. Serra's work in the 1990s also continued to engage with the theme of site specificity. "The Matter of Time," a monumental installation at the Guggenheim Bilbao, consists of eight large steel sculptures arranged in a long gallery. This work, like many of Serra's installations from this period, is designed to provoke a range of emotional responses as viewers navigate the space, from claustrophobia and dread to release and exhilaration. The fabrication and installation of these pieces relied on sophisticated digital modeling and engineering techniques, underscoring the technical complexity and precision involved in realizing Serra's vision​ (Metropolis Magazine)​. Throughout the 1990s, Serra's work maintained a focus on the interplay between sculpture, space, and the viewer. His sculptures from this period are not just objects to be looked at but environments to be experienced, emphasizing the physical act of moving through space as an integral component of the work. This emphasis on the phenomenological aspects of sculpture has solidified Serra's place as one of the most important and influential sculptors of his time, continually pushing the boundaries of what sculpture can be and how it can engage with the world​ (TheCollector)​​ (The Art Story)​​ (Artsy)​.