rratherbeflying

my house is in Okla, built in 1927. Gingerbread brick, hardwood floors, glass doorknobs, etc just to let you know what i am looking at. In the process of installing insulated drapes, (the rods, bo be specific), i drilled through plaster, then wood slats, then..... metal? something really hard before pentrating free space. any idea of what i encountered without having to replace a wall? i am looking at doing some plaster repair work in another room and would appreciate a heads-up on what i am in for before starting in the spring. i am sure there will be no insulation, but what in the world could be behind the plaster, then wooden slats that would be so resistant to a drill bit? oh! the bit was blackened after drilling whatever this is.......