Venetians rebelled against the Austrian Empire on 17 March 1848. The Republic of San Marco was founded on 22 March 1848 and Daniele Manin became its president. However, on 22 August 1849, the Austrian army overthrew the Republic of San Marco and re-established the supremacy of Austria in Venice. Immediately after the Austrians entered Venice on 27 August, President Daniele Manin and 39 revolutionary leaders fled Italy. 

Image: La proclamazione della Repubblica di San Marco, Marzo 1848, 1850, by Sanesi. This image is part of the public domain and is available on Wikimedia Commons.

Additional Reading

Cunsolo, Ronald. S. "Venice and the Revolution of 1848-49." in James Chastain et al. Encyclopedia of Revolutions of 1848, Ohio University, 27 Oct 2004, www.ohio.edu/chastain/rz/venrev.htm