ISAURIA. - It is the westernmost province of the patriarchate of Antioch, and in the ecclesiastical geography of the Byzantine era it comprises only a part of the previous Roman province, roughly the valleys of the Lamos and the Kalykandos and the mountainous massif between the latter and the sea. Its archaeological exploration is incomplete. The metropolis of Isauria is Seleucia, near which arose the most important sanctuary dedicated to the cult of St. Thecla, which had supplanted that of the demon Sarpedon and the goddess Athena, consisting of a martyrion and monasteries enclosed within a fortified wall to protect against brigand attacks. The sanctuary attracted a very large number of pilgrims from every region. The miracles of St. Thecla also recall a chapel of the Saint at Selinunte, built on an acropolis and which often defended the city against enemy attacks; another monastery of St. Thecla, known through an inscription, existed at Diocesarea, and a sanctuary at Dalisandea that was a famous place of pilgrimage almost as much as that near Seleucia. The mountainous character of the region protected the Christian communities in the first centuries of the Muslim invasion, so that representatives of the ancient bishoprics appear in part even at the Seventh Council, and George of Cyprus, the *Nea Tactica* and the *Notitia Antiochiana* list up to eight names of episcopal sees.
The most important group of monuments in Isauria is that of the sanctuary of St. Thecla near Seleucia, in the locality now called Meriamlik: a large three-aisled basilica divided by columns, probably built in the second half of the 5th century and later modified; a cave beneath it transformed into a church; a domed basilica over the central nave, probably a foundation of Emperor Zeno (474-91), and a little further away the North Church. Of the greatest importance is this domed basilica, which documents a new conception of architectural space in the evolution of basilican forms in Seleucia—an ancient Roman temple had been transformed into a church with the substitution of an apse on one of the minor sides. The basilica of St. Thecla is notable not only for its great size, but chiefly because the two rooms flanking the apse in the manner of Syria are each provided with an apse according to a structure characteristic of north-central Syria (cathedral of il-Anderin, martyrion and Basilica B of Resafa).
At the northern end of the valley of the Kalykandos, near the village of Hoğa Kalesi, there stands another very important church: a three-aisled basilica of perfect construction in hewn stone, with technique (even in the decoration) distinctly Syrian; the central nave is divided into two parts by transverse arches, and above that in front of the presbytery rises a tower which, at its upper level, above the matroneum, has chamfered corners with four niche-like recesses supported by columns, similar to those of the side chambers at the apse of the basilica of St. Sergius at Resafa and at the Red Monastery near Sohag, all monuments of the mid-5th century. Also of distinctly Syrian plan with the apse flanked by two chambers are the large church with matroneum at Gâmbazli and one at Tapureli; whereas, on the other hand, a church at Olba and two at Sok Örem (Korasion) are connected with structures widespread in Cilicia, having, that is, a room behind the apse, in the first case also provided with two apses. Its liturgical function is unknown. A church at Olba and one at Tapureli have only a diaconicon. All these three-aisled basilicas are provided with a narthex, and at Meriamlik, both in the domed basilica and in the North Church, there is also an atrium, evidence of the penetration of Hellenistic elements into a region that may be considered the extreme outpost of Syrian architecture toward the northwest.