Hal,

I will be journeying myself to Florence in July, so your question has
prompted me to do a quick Google search.

Here are two hits.

http://www.twainquotes.com/19031109.html
The New York Times, November 9, 1903
Mark Twain's Villa Near Florence.
FLORENCE, Nov. 8. - Samuel L. Clemens (Mark Twain) and his family,
accompanied by George Gregory Smith, have arrived here and taken
possession of the Villa Quarto, three miles and a half from the city. The
villa was formerly the property of a Russian Grand Duchesse and was
afterward occupied by the King of Wurtemberg. It is now owned by Count
Reybaudi Massiglia, Italian Minister to Persia, who was formerly Consul at
Philadelphia, where he married Miss Paxton.

http://www.twainquotes.com/interviews/critic1904.html  pictures and text,
including
The most important personage in the group is Mark Twain, as the villa of
his selection is the most sumptuous of them all. The Villa di Quarto lies
in a charmingly picturesque spot not far from Florence. It has sheltered
the most illustrious people, and all of them have admired its beauty, both
natural and artificial -- its magnificent grounds with broad avenues,
fountains, and smiling gardens. An idea of it size -- the circumference of
the park is over two miles -- may be given by saying that at one time a
Russian princess lived there with a suite of one hundred persons. Victor
Emanuel II visited it frequently, as it is close to the royal country seat
of La Petraia.