The lagoon facade as we see it now, with its slender arches above the sturdy arches, thus dates from the beginning of the fifteenth century, and this design gave the key to the builders of later Venice, as a voyage of the Grand Canal will prove.
It was the great Doge Tommaso Mocenigo (1413-1423) who urged upon the Senate the necessity of completing the palace.

In 1424 the work was begun.

Progress was slow and was hindered by the usual fire, but gradually the splendid stone wall on the Rio del Palazzo side went up, and the right end of the lagoon facade, and the Giants' Stairs, and the Piazzetta facade, reproducing the lagoon facade.

The elaborately decorated facades of the courtyard came later, and by 1550 the palace was finished.

The irregularity of the windows on the lagoon facade is explained by this piecemeal structure.