The motto on the sundial is SOL LUCET OMNIBUS, "The sun shines for everyone / on everything." The words can be found in the Satyricon of Petronius:
Non commune est, quod natura optimum fecit? Sol omnibus lucet. Luna innumerabilibus comitata sideribus etiam feras ducit ad pabulum. Quid aquis dici formosius potest? In publico tamen manant.
Is Nature's best work not common to all? The sun shines for everyone. The moon accompanied by countless stars leads even wild beasts to their food. What can be said to be more beautiful than the water? Yet it flows for our common use.
The photo is by Gustavo F. Porto de Mello at Wikimedia Commons: