Le Trône is the former name of the place de la Nation. The concerned trône ("throne") was used by king Louis XIV and his wife Maria-Theresa of Austria, in August 1660... a huge seat, overturned during the Revolution, when they renamed the place Place du Trône renversé... which means “Square of Upside down Throne”! You know what? The sinister shade of the guillotine stood there...
Well, what is this barrière? A wall raised just before the Revolution, in order to collect a tax from goods which entered in the city: a toll gate! This barrière was raised by architect Ledoux in 1788: a chap who also erected the two detached houses and the 30 metres high columns. Golden statues were added in the reign of Louis-Philippe: they are portraits of Philip Augustus and Louis XI (made by Etex and Dumont).