Baldassare Peruzzi (1481-1536)
originally a painter, perspectivist.
to Rome in 1505 from Siena.

Villa Farnesina for Agostino Chigi, 1509-11.

Much of his work is epehemeral in nature, stage sets and pageant
     decoration.

Baneo di S. Spirto in Rome:

Antonio Tempesta's Map of Rome:

Assistant to Antonio da Sangallo at St. Peters, 1520. Produced my
     drawings and schemes, highly experimental.

1527 (Sack of Rome) returns to Siena, only sporadically in Rome
     thereafter. Projects for S. Petronio, Bologna, S. Giacomo degli Incurabili, a
     hospital in Rome, remodelling projects for dome of Siena cathedral
     and the church of S. Domenico in Siena.
Palazzo Massimi delle Colonne, Rome, begun 1532.

Antonio da San Gallo, the younger (1484-1546)
nephew of Giuliano and Antonio the elder
first appears as carpenter who helps with centering for Bramante's
     arches for the crossing of St. Peter's, 1509
1516, appointed assistant to Raphael at St. Peter's. Evolved from
     carpentario to architetto. His bookplate in his copy of Fra
     Giocondo's 1511 edition of Vitruvius dated 1520.
Reconstruction of a Roman house form Fra Giocondo's Manuscript:

Architect in Chief of St. Peter's 1520 (succeeding Raphael) and of all
     other building projects in the papal state, til his death in 1546.

military architect. 1534, Fortezza da Basso, Florence.
Porta di Santo Spirito, Vatican, Rome.
Zecca, or Papal Mint, c. 1530.

Porta Ardeatina, Bastion, 1542.

For comparision medevil fortifications of Montagnana.

Michelangelo's Scheme for defenceworks.

1539, Model of St. Peter's. approved by pope and made binding on
     subsequent architects. (In the fact, Michelangelo with papal
     support, revised the scheme dramatically.) The new scheme
     attempted to resolve the conflict between a centralized and a
     longitudinal plan, It reinforced the piers supporting the dome, and
     raised the floor of the church 3.2 meters. It uses a dome of
     pointed section, like Florence and unlike Bramante's scheme.
     Double dome gives a more hemispheric profile to exterior. Little of
     Antonio's work survives in building. Michelangelo scheme wiped
     out much.

Benvenuto Cellini (Sculptor and diarist of 16th c explained Antonio's
     limited success to his training as a carpenter, rather than as a
     painter, ie not an artist. From this time forward, with the
     exception of Michelangelo, architecture will be a seperate
     profession.) Antonio was a builder, uniquely capable, systematic,
     well organized. He grasped Bramante and Raphael's idiom. He
     sought system through Vitruvius. His strength was not
     imagination.
As head of papal works and St. Peter's Antonio had the most
     extensive practice of his time. He had many assistants and left
     many drawings.
Palazzo Farnese, begun 1517 for Cardinal Alexander Farnese who
     became pope as Paul III in 1534. The project, finalized in 1541,
     now becomes even more grand than it had been. Enlarged stair,
     court, whole. Grand reception room. Three aisle vestibule and
     ground level elevation of court are elements from the original
     scheme. Facade, also by Sangallo, is 1541 scheme. Michelangelo
     won competition for facade cornice in 1546

Plan of Rome surounding the Pal. Farnese after the project's compleation: