Definition of "expanse"

That large room had always awed Ivor: even as a child he had never wanted to play in it, for all that it was so limitless, the parquet floor so vast and shiny and unencumbered, the windows so wide and light with the fairy expanse of Kensington Gardens.

1922, Michael Arlen, “1/1/3”, in “Piracy”: A Romantic Chronicle of These Days‎