An delegation of U.S. House Democrats poised to become prosecutors marched across the Capitol Monday night to deliver a single article of impeachment against Donald Trump, triggering the start of an unprecedented trial of the former president.

The nine House impeachment managers selected by Speaker Nancy Pelosi delivered the impeachment article to the secretary of the Senate at about 7 p.m., with lead manager Jamie Raskin of Maryland reading it aloud on the floor of the chamber.

Trump is the first U.S. president to have been impeached twice and will be the first to be tried after leaving office. Delivery of the impeachment article, followed on Tuesday by the swearing in of senators as jurors, formally signals the start of the proceedings, though arguments won’t begin until the week of Feb. 8.