From Dom Gueranger’s Liturgical Year: 

In the fourth century of our era, the cessation of persecution seemed to give the world a foretaste of its future entrance into eternal peace.  ‘Glory to the Almighty!  Glory to the Redeemer of our souls!’ wrote Eusebius at the opening of the tenth and last book of his history.  Himself a witness of the triumph, he describes the admirable spectacle everywhere displayed by the dedication of the new sanctuaries.  In city after city the bishops assembled, and crowds flocked together.  From nation to nation the goodwill of mutual charity, of common faith, and of recollected joy, so harmonized all hearts that the unity of Christ’s Body was clearly manifested in these multitudes animated by the same inspiration of the Holy Ghost.  It was the fulfilment of the ancient prophecies: the living city of the living God, where all, whatever their age or sex, praise together the Author of all good things.  How solemn were then the rites of the Church!  The complete perfection therein displayed by the pontiffs, the enthusiasm of the psalmody, the inspired readings, the celebration of the ineffable mysteries, formed a divine pageantry.*

Constantine had placed the imperial treasure at the disposal of the bishops; and he himself stimulated their zeal for what he called in his edicts the work of the churches.#  Rome, the place of his victory by the cross, the capital of the now Christian world, was the first to benefit by the prince’s munificence.  In a series of dedications, to the glory of the holy apostles and martyrs, Sylvester, the pontiff of peace, took possession of the eternal city in the name of the true God.

To-day is the birthday of the mother and mistress of churches, called ‘of our Saviour, Aula Dei (God’s palace), the golden basilica’; it is a new Sinai, whence the apostolic oracles and so many Councils have made known to the world the law of salvation.  No wonder this feast is celebrated by the whole world. 

As we live in a time so very different from the golden age wherein it was dedicated, may we thank God for His providence both for the establishment and the preservation of St. John Lateran, and the apostolic succession it in some measure represents.

*Eusebius, Hist. eccl. x, 1-4.  # Ibid. De vita Constantini, ii, 45-46.