Library Eusebius of Caesarea Preparation for the Gospel
Book 9, Chapter 36
'THE author of the Metrical Survey of Syria says in his first book that Jerusalem lies upon a lofty and rugged site: and that some parts of the wall are built of polished stone, but the greater part of rubble; and that the city has a circuit of twenty-seven furlongs, and that there is also within the place a spring which spouts up abundance of water.
English translation by E. H. Gifford, Eusebii Pamphili Evangelicae Praeparationis Libri XV (Oxford, 1903). Public domain. Digital text via Roger Pearse / tertullian.org.