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.
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.
Arch of Janus Quadrifrons
Basilica Santa Agnese
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.
18 August -- the feast of Saint Helena
Did the Donatist Controversy play a role in how Helena's "conversion" to Christianity was [incorrectly?] recorded by Eusebius?
Re: Cathedral of Tyre 314?
...in the specific case of the Cathedral of Tyre, the date of dedication is still significant because of its closeness to the (so-called) Edict of Milan (313) enacted between Constantine and Licinius. [I'm writing on the fly here, so I don't have the exact date of the Edict at hand.] As I recall, it was at the same time in Milan that most scholars believe that Constantine's half-sister Constantia was betrothed to Licinius as well. In this light, I personally believe any three of the above personalities could have been directly involved with the renewed church building at Tyre. Constantia surely died a Christian, and was indeed very religiously active during and after the years of her marriage to Licinius. For example, I just recently learned that Constantia was both present and actively vocal at the Council of Nicaea. She was also very close (friends) with Bishop Eusebius of Nicomedia (not to be confused with Eusebius of Caesarea who wrote the Vita Constantini).
My thesis all along is that Constantine of course was ruler during the Christian church building boom of the 310s and 320s, but that the real champion of the church building cause was indeed Helena, and, to a lesser extent, other high Imperial women like Eutropia, and perhaps even Constantia, and maybe later even Constantina, Constantine's daughter. The Helena and Eutropia chapters of the Vita Constantini Book III are, I believe, indicative of what happened and how it (the church building) happened. In simple terms, Helena's activities had Constantine's automatic sanction, including full access to the imperial treasury, thus the expeditiousness of the church building in Rome during the 310s and the same expediency of church building in the Holy Land 325 and right after. Furthermore, a careful reading of Constantine's account of his letter from Eutropia regarding the holy site at Mamre (VC III 52) further discloses the outright gleefulness that the Imperials came to savor in their Christian church/architecture efforts.
I am looking at this distinct church building occurrence from the view point of a modern registered architect, and I'm most intrigued by how quickly it all happened. It doesn't matter what age or era we talk about when it comes to the real time it takes to erect buildings. That so much was very quickly accomplished, for example, in Rome in the years just after late October 312, implies, to me at least, that someone was there supervising, and even planning, the architectural activities, otherwise it just would not have happened with the obvious careful intentionality that it did. My candidate for the person "in charge" is Flavia Julia Helena Augusta. (For contexts sake, remember Constantine himself spent a total of only a few months in Rome during the years between 28 October 312 and 3 August 325.)
So, back to the Cathedral of Tyre. What this church may represent is the (just pre-Constantinian)prototype for basilican church design of the early fourth century. That such a prototype should come from the East is also significant in that other architectural innovations at that time also seem to have come from the East. For example, the brickwork of the Aula Palatina, the Constantinian throne hall at Treves (Trier, Germany) circa 306-312, according the Ward-Perkins, exhibits masonry technique up until then only known in the East. So again, can anyone verify the date of the dedication of the Cathedral of Tyre in Phoenicia?
Catherdral of Tyre 314?
Another possibility, of course, is that Constantine simply took credit for the church (or Eusebius et al. gave him credit) after the fact.
I don't know that there is any late antique reference to Constantine being at all connected with the re-building of the Cathedral of Tyre. It appears to be more of a "modern" connection that has been made.
Probably because there is hardly any physical evidence left of the pre-Constantine Christian churches throughout the East (e.g., the church of Nicomedia that was right across from Diocletian's palace there), it seems often overlooked that there indeed were Christian churches in existence prior to Constantine's rulership. Constantine certainly cannot be given credit for the original erection of the church of Nicomedia, nor can the earlier Imperial hierarchy for that matter. It seems only logical that the Christian's themselves, along with their priestly hierarchy, were already responsible for building churches in the East prior to 28 October 312. The case in Rome seems different, however, in that prior to October 312 actual churches did not exist, rather only catacombs and domestic gathering places. Thus, in the case of the Cathedral of Tyre, it could just as well have been the Christians of Tyre themselves that straight away after the Edict of Milan (February 313), i.e., when the Christians in the East got back what was taken from them during the Great Persecution, set out to rebuild their church that was destroyed under Diocletian.
For the record, Constantine spent most of the year and a half after the Edict of Milan at Trier, which is more or less Tyre's opposite extreme in the Empire.