Syria is thought to have one of the world's largest stockpiles of chemical weapons. Those weapons have recently been used against Syrian civilians, compelling the world to respond to the country's two-plus-year civil war. So it's worth taking a step back to understand the weapons that have become so central to the Syrian crisis and how they work. This infographic, produced by The Washington Post, is a great introduction.

The infographic explains what chemical weapons do to people – it's pretty horrible – and how they're delivered. It also explains how chemical weapons are destroyed – a crucially important subject now that the U.S. and Russia have agreed in principle to a deal to remove Syria's chemical weapons outright, which would be no easy task in the middle of a civil war.