Ludwig Mies van der Rohe ( MEESS; German: [mi:s]; born Maria Ludwig Michael Mies; March 27, 1886 - August 17, 1969) was a German-American architect. He is commonly referred to and was addressed as Mies, his surname.

Mies designed a series of four middle-income high-rise apartment buildings for developer Herbert Greenwald: the 860-880 (which was built between 1949 and 1951) and 900-910 Lake Shore Drive towers on Chicago's Lakefront. These towers, with facades of steel and glass, were radical departures from the typical residential brick apartment buildings of the time. Mies found their unit sizes too small for him, choosing instead to continue living in a spacious traditional luxury apartment a few blocks away. The towers were simple rectangular boxes with a non-hierarchical wall enclosure, raised on stilts above a glass-enclosed lobby.  The lobby is set back from the perimeter columns, which were exposed around the perimeter of the building above, creating a modern arcade not unlike those of the Greek temples. This configuration created a feeling of light, openness, and freedom of movement at the ground level that became the prototype for countless new towers designed both by Mies's office and his followers. Some historians argue that this new approach is an expression of the American spirit and the boundless open space of the frontier, which German culture so admired.  Once Mies had established his basic design concept for the general form and details of his tower buildings, he applied those solutions (with evolving refinements) to his later high-rise building projects. The architecture of his towers appears to be similar, but each project represents new ideas about the formation of highly sophisticated urban space at ground level. He delighted in the composition of multiple towers arranged in a seemingly casual non-hierarchical relation to each other.  Just as with his interiors, he created free flowing spaces and flat surfaces that represented the idea of an oasis of uncluttered clarity and calm within the chaos of the city. He included nature by leaving openings in the pavement, through which plants seem to grow unfettered by urbanization, just as in the pre-settlement environment.

Answer the following question by taking a quote from the article: What  material were they built from?
These towers, with facades of steel and glass, were radical departures from the typical residential brick apartment buildings of the time.