The Library of Congress first existed in The Capitol in 1800, as a few volumes bought from Philadelphia, and then occupied various spaces throughout the building until the British burned it down in 1814. Thomas Jefferson offered to sell his own personal library so this was purchased in 1815. A second fire on Christmas Eve 1851 destroyed two thirds of the 6487 books so it was decided a new building had to be found. The Jefferson Building was completed in 1897 with its 23 carat gold plated dome and a guidebook for visitors. It was dubbed the" largest, costliest and safest" library in the world. It was a state of the art structure, using latest technology, and a Temple of the Arts.
but this link will explain much plus additional images.
And here - On These Walls.