February 27, 1933, Berlin:

The Reichstag (home of the legislature), in ashes after arson for which Marinus van der Lubbe took credit, became a rallying point on which the Nazis gained power.

It seems clear that the arsonist had help, probably from the Nazis themselves. In short, they burned the Reichstag and then said "Something must be done about all this anarchy! The Reichstag has been burned!".

Acts of terrorism, most recently the fall of the World Trade Center on September 11, 2001, have sometimes been compared to the Reichstag fire. The implication is that the acts were committed to create a harsh reaction -- martial law, retaliatory war against usual suspects, and so on. Fortunately, these comparisons have generally been based more on fear than on evidence.

SOURCE: http://www.barnsdle.demon.co.uk/hist/fire.html