G7 - the "Group of Seven" countries - came together in 1975 as the seven most important industrialized nations at the time.
These seven countries are the US, the UK, France, Germany, Italy, Japan and Canada. In 1998 Russia was added and the group expanded to G8, before it was excluded again in 2014 after Russia's annexation of the Crimean peninsula.
Traffic was at a standstill in the Italian capital, where parts of the city center closed off for the visit of Chinese president Xi Jinping. He kicked off his European trip in Italy, whose populist government is eager to boost trade with China.
Chancellor Merkel has said trade accounting methods are outdated and need revision. Done differently, figures show the US had a $14 billion surplus rather than $153 billion deficit with the European Union in 2017.