Until the recent establishment of constitutional government in Turkey it was impossible to obtain permission to study this church in a satisfactory manner, so jealously was even entrance into the building guarded. The nearest approach to anything like a proper examination of the building was when Salzenberg was allowed to visit the church in 1848, while the church of S. Sophia was undergoing repairs under the superintendence of the Italian architect Fossati. But the liberty accorded to Salzenberg was not complete, and, consequently, his plan of the church published in his _Altchristliche Baudenkmäler von Konstantinopel_ is marred by serious mistakes. Happily the new Government of the Empire is animated by an enlightened and liberal spirit, and at the request of His Excellency Sir Gerard Lowther, H.B.M. Ambassador to the Sublime Porte, permission was granted to the Byzantine Research and Publication Fund to have the church examined as thoroughly as its condition allowed, and to make all the plans, drawings, and photographs required in the interests of a scientific knowledge of its architectural character. The Byzantine Research and Publication Fund was fortunate in having as its president, Edwin Freshfield, LL.D., so long distinguished for his devotion to Byzantine archaeology, and it is mainly due to his generosity that the means necessary for carrying on the study of the church were provided. The society was, moreover, most happy in being able to secure the services of an architect in Mr. W. S. George, who already possessed considerable experience in the investigation of Byzantine buildings at Salonica and elsewhere. Fortunately, also, the building was at the same time placed under repair, in view of its conversion into a museum of arms, thus affording exceptional facilities for the erection of scaffolding and the removal of plaster and other obstructions. Mr. George gave nearly five months to the study of the church, and the results of his careful investigations will appear in a monograph to be published by the Byzantine Research and Publication Fund. But with great courtesy, in view of the fact that I was engaged on the present work, and also because I waived my own application for leave to study S. Irene in favour of the application made by the Byzantine Fund, I have been allowed to anticipate that monograph by making use of some of the results of Mr. George's investigations. For this permission I am very grateful, as it will add much to the value of this volume. I visited the church frequently while Mr. George was at work upon it, and my account of its architectural features is based entirely upon the information he then kindly supplied, and upon the notes he has communicated to me since his return to England. [Illustration: PLATE XIX. (1) S. IRENE. VAULTING AT THE NORTH-WEST CORNER OF THE ATRIUM. (2) S. IRENE. THE NORTHERN ARCH OF THE MAIN DOME, SEEN FROM THE SOUTH GALLERY. _To face page 92._]