February: Constantine and Licinius meet in Milan where the two emperors agree on a common religious policy whereby Licinius subsequently grants the Christians within the eastern Empire the same toleration already granted Christian's throughout the western Empire, including the restitution of confiscated Christian property--the so-called Edict of Milan. Licinius and Constantia are married.
Helena commences the restoration of thermal baths near the palatium Sessorianum.
30 April: Licinius defeats Maximinus Daia near Adianople (in Thrace). Licinius is now sole ruler in the eastern Empire, while Constantine is sole ruler in the western Empire.
Cathedral of Tyre -- answers
I found some answers to the questions regarding the Cathedral of Tyre in T.D. Barnes' Constantine And Eusebius pp. 161-62. For brevity's sake, here are the facts:
1. it was Maximinus Daia in Spring/Summer 313 that "granted the right to [re]building churches," and the source for this is in Eusebius Ecclesiastical History Book 9.
2. Eusebius "in a speech which forms the greater part of Book Ten of the History; he delivered the speech in Tyre about 315, when the rebuilt basilica was dedicated."
I think it is now safe to say that the rebuilt Cathedral of Tyre should not be directly attributed to Constantine. This then seems to open further implication that the churches Constantine IS responsible for are of a distinct set of churches that are special because of their unprecedented Imperial initiation and funding.
2 October: A synod in Rome regarding the Donatist controversy convenes within the Lateran Palace, an imperial estate since the time of Nero, which Constantine gave to Pope Miltiades as a (papal) residence. This is also the earliest possible date for the initial construction of the Basilica Constantiniana (later the Basilica of Saint Giovanni in Laterano). The Latern Palace was next to the fundus Laurentus, extensive imperial property mostly southeast of the Aurelian Wall which became the estate of Helena sometime after 312.
North of S. Croce in the vigna Conti are the ruins of some thermae, including a piscina, which are known to have been restored by Helena after a fire and are therefore called the thermae Helenae. Complete plans of these baths, made by Palladio and Sangallo in the sixteenth century, are in existence, but the ruins themselves are very meager.
Samuel Ball Platner, The Topography and Monumants of Ancient Rome (Boston: Allyn and Bacon, 1904), p. 448.
Basilica of Maxentius/Constantine, Rome (A.D. 310-313).
Plan and longitudinal section of an antique edifice in Rome, called the
Temple of Peace Basilica of Maxentius/Constantine.
Portion of the interior of the Temple of Peace [ actually Basilica of Maxentius/Constantine], Rome. The architrave profiles over each column.