Located behind the Hippodrome, Little Hagia Sophia (Church of Saints Sergius and Bacchus) is one of Istanbul’s oldest and most overlooked treasures. Built by Emperor Justinian I and Empress Theodora in the 6th century, it features an innovative octagonal plan, marble columns, and symbolic Byzantine motifs like acanthus leaves, pinecones, and imperial monograms. Once part of a twin-church complex, it predates Hagia Sophia and inspired its design. Converted into the Küçük Ayasofya Mosque, this architectural jewel still radiates a sacred calm, offering visitors a glimpse into the spiritual and artistic heart of early Byzantine Constantinople.