Almost all the Byzantine churches in Thessaloníki are located in the central districts or on the slopes heading up towards the Upper Town. Under the Turks most of the buildings were converted for use as mosques, a process that obscured many of their original features and destroyed (by whitewashing) the majority of their frescoes and mosaics. Further damage came with the 1917 fire and, more recently, with the 1978 earthquake. Restoration seems a glacially slow process, guaranteeing that many of the sanctuaries are locked, or shrouded in scaffolding. Nevertheless, the churches of Thessaloníki remain an impressive group. The main ones are described below, apart from the two most important churches, Ayía Sofía and Áyios Dhimítrios, given their place in the main city account. All are free to enter.

One of the most central is the eleventh-century Panayía Halkéon church (daily 7.30am– noon), a classic though rather unimaginative example of the "cross-in-square" form, nestling on Egnatía at the southwestern corner of Platía Dhikastiríon, amid luxuriant palms, cypress and pines. It is worth popping inside to see the fragmentary frescoes in the cupola and some fine icons. As the Greek name indicates, it served during the Ottoman occupation as the copperworkers' guild mosque; the only remnant of this tradition is the handful of kitsch-copper souvenir shops just across the street.

Several blocks east, and tucked away just out of sight north of the boulevard, the restored, fifth-century, three-aisled basilica of Panayía Ahiropíitos (daily 7am– noon & 4.30–6.30pm) is the oldest in the city, featuring arcades, monolithic columns and often highly elaborate capitals – a popular development begun under Theodosius. Only the mosaics inside the arches survive, depicting birds, fruits and vegetation in a rich Alexandrian style.

Around Áyios Dhimítrios are several more churches, utterly different in feel. To the west along Ayíou Dhimitríou is the church of Dhódheka Apóstoli (daily 8.30am– noon & 5–7pm), built with seven more centuries of experience and the bold Renaissance influence of Mystra. Its five domes rise in perfect symmetry above walls of fine brickwork, while inside are glorious fourteenth-century mosaics, among the last executed in the Byzantine empire. High up in the arches to the south, west and north of the dome respectively are a Nativity, an Entry into Jerusalem, a Resurrection and a Transfiguration.

A short climb up Ayías Sofías is Ósios Dhavíd (Mon– Sat 9am– noon & 4–6pm), a tiny fifth-century church on Odhós Timothéou. It doesn't really fit into any architectural progression, since the Ottomans demolished much of the building when converting it to a mosque. However, it has arguably the finest mosaic in the city, depicting a clean-shaven Christ Emmanuel appearing in a vision, surrounded by the Tetramorphs or symbols of the four Gospels. The four Rivers of Paradise, replete with fish, flow from beneath Christ, lapping the feet of the prophets Ezekiel and Habakkuk, who respectively cringe in terror and ponder at the revelation. Ask the curator to switch on the floodlights for a better view; a small donation for a candle will be appreciated.

Farther east in Kástra, to the north of Atatürk's house, on Irodhótou, fourteenth-century Áyios Nikólaos Orfanós (Tues– Sun 8.30am–2.45pm) is a diminutive, much-altered basilica; the imaginative and well-preserved frescoes inside are the most accessible and expressive in the city. In the south aisle, Áyios Yerásimos of Jordan is seen with anthropomorphic lions, while Christ's miracles are set forth in a row above. The naos is devoted to episodes from the Passion, in particular the rarely depicted Christ Mounting the Cross and Pilate Seated in Judgement at a wooden desk. Above the Virgin Platytera in the apse conch looms the equally unusual Áyion Mandílion, an image of Christ's head superimposed on a legendary Turin-style veil sent to an ancient king of Anatolian Edessa. Around the apse is a wonderful Niptir (Christ Washing the Disciple's Feet), in which it is thought the painter inserted (in lieu of a signature) an image of himself at the top right above the conch, riding a horse and wearing a white turban.