After the visit to the Piazza dei Miracoli, I recommend going to the Piazza dei Cavalieri. You can get there walking along Via Santa Maria, and then turning right to Via dei Mille.
Piazza dei Cavalieri, or the Knights Square, used to be the the administrative center of Pisa during the middle ages. In the 16th century, the square was remodeled, and became a symbol of the power of the Medici family in Pisa.
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