In his picture of 'Dido building Carthage,' he painted imaginary palaces, rivers, and stately ships, in the same cool colouring as Claude, and bequeathed his picture to the National Gallery, on condition that it should hang for ever between two pictures by Claude to challenge their superiority.

Opinions are divided as to the rank of Turner's 'Carthage,' so when you go to the National Gallery, you must look at them both and prepare to form a preference.
Turner was incited to this rivalry with Claude by the popularity that painter enjoyed among English collectors of the day, who were less eager to buy Turner's great oil-paintings than those of his predecessor.
Incidentally this rivalry was the origin of the great series of etchings executed by or for him, known as _The Book of Studies (Liber Studiorum)_.

This book was suggested by Claude's _Libri di Verita_, six volumes of his own drawings (of pictures he himself had painted and sold) made in order to identify his own, and detect spurious, productions.

But Turner's book was designed to show his power in the whole range of landscape art.

The drawings were carefully finished productions, work by which he was willing to be judged, and many of them he etched with his own hands.