It's a pity that Thessaloniki's two most important churches -- Ayia Sofia (Holy Wisdom) and Ayios Dimitrios (St. Demetrios) -- are both heavily restored. Still, each is worth visiting for its importance in the city's history and for its fine mosaics, although both lack the pleasantly dusty ambience and odor of sanctity found in Thessaloniki's less heavily restored churches.
Thessaloniki's 7th-century Ayia Sofia was inspired by the emperor Justinian's famous 6th-century church of Ayia Sofia in Constantinople, although there may have been a modest 4th-century church here. Like the majestic Ayia Sofia in Constantinople (today's Istanbul), Salonika's namesake has an impressively large -- in fact, an astonishingly large and astonishingly technical -- dome. The ornately carved marble columns supporting the dome were pillaged from earlier monuments (as they were so often in antiquity and throughout the Byzantine era).
Fortunately, some of Ayia Sofia's original mosaics have survived. The Ascension, with an oddly foreshortened Christ (supported by young angels), and the Virgin Mary with the infant Jesus are especially fine. Look carefully at the mosaics, and you'll notice that some show only crosses and stars and have no human representations. These date from the 8th-century Iconoclastic period, when there was a ban on showing the human figure in religious art. The Iconoclasts destroyed many earlier works of art, including sacred icons, and left us with the word "iconoclast" to describe someone who destroys the past or challenges tradition.
Ayia Sofia Square is one of Thessaloniki's most important, squares. Many of its finest houses were destroyed in the fire of 1917, which damaged Ayia Sofia church as well. Others suffered extensive damage during World War II. A service of thanksgiving was held here when the Allies liberated the city on November 2, 1944. Today, much of Thessaloniki heads here for Easter and other important services. Keep an eye out for the "red house" at 31 Ayias Sofias, built in 1925 for a wealthy industrialist; across the street is the Terkenlis pastry shop, which also has sandwiches and a wide variety of delicious ice creams. The pastry shop is an excellent spot to rest and refresh yourself after you see the church; until then, you can check out the goodies and pinpoint other Terkenlis branches in Thessaloniki at www.terkenlis.gr.