From Edmund Bacon's Design Of Cities:
Any really great work has within it seminal forces capable of influencing subsequent development around it, and often in ways unconceived of by its creator. The great beauty and elegance of Brunelleschi's arcade of the Foundling Hospital... found expression elsewhere in the Piazza della Santissima Annunziata, whether or not Brunelleschi intended this to be so.The first significant change in the square, following the completion of the arcade in 1427, was the construction of the central bay of the Santissima Annunziata church. This was designed by Michelozzo in 1454 and is harmonious with Brunelleschi's work. However, the form of the square remained in doubt until 1516, when architects Antonio da Sangallo the Elder and Baccio d'Agnolo were commissioned to design the building opposite to Brunelleschi's arcade. It was the great decision of Sagnallo to overcome his urge toward self-expression and follow, almost to the letter, the design of the then eighty-nine-year-old building of Brunelleschi. This design set the form of Piazza della Santissima Annunziata and established, in the Renaissance train of thought, the concept of a space created by several buildings designed in relation to one another. From this the "principle of the second man" can be formulated: it is the second man who determines whether the creation of the first man will be carried forward or destroyed...The quality of Piazza della Santissima Annunziata is largely derived form the consummate architectural expression that Brunelleschi gave the first work, the Innocenti arcade, but it is really to Sagnallo that we owe the piazza in its present form. He set the course of continuity that has been followed by the designers there ever since.