Eight UNESCO World Heritage monuments occupy less than two square kilometres of Ravenna's centro storico. The Basilica di San Vitale alone preserves 600 square metres of sixth-century tesserae — Byzantine glass mosaics that Emperor Justinian commissioned in 547 CE, the same year his armies reclaimed Italy from the Ostrogoths. The Mausoleum of Galla Placidia, built three generations earlier, holds the oldest intact mosaics in the Western Roman Empire: a midnight-blue vault studded with 570 gold stars, each tessera hand-cut from Venetian smalto glass. Ravenna became the capital of the Western Roman Empire in 402 CE, when Emperor Honorius moved his court from Milan to escape Gothic sieges. For the next three centuries, the city stood at the fulcrum of three empires — Roman, Ostrogothic, and Byzantine — and each dynasty left its mark in mosaic. The Arian Baptistery, consecrated under Theodoric the Great around 500 CE, displays a Christ figure emerging from the Jordan River in pale green and gold, his body rendered in classical Roman naturalism. Fifty years later, Byzantine mosaicists working at Sant'Apollinare Nuovo replaced Theodoric's Arian iconography with Orthodox saints, but left the architectural borders intact. The result is a visual palimpsest: Arian theology overlaid with Byzantine dogma, separated by a single generation. The combined ticket covers five monuments — San Vitale, Galla Placidia, Sant'Apollinare Nuovo, the Neonian Baptistery, and the Archiepiscopal Chapel — each within walking distance. San Vitale's apse mosaics, executed by North African craftsmen, use perspective techniques that would not reappear in Western art until Giotto painted the Scrovegni Chapel in 1305. The Basilica of Sant'Apollinare in Classe, three kilometres south, adds a sixth site: twenty-four processional sheep rendered in white Carrara marble tesserae, marching toward an apse where Christ appears as a jewelled cross above a field of Persian flowers. Ravenna's mosaics survived because the city declined. After Charlemagne stripped its marbles for his Palatine Chapel in 800 CE, Ravenna became a backwater. No Baroque renovations. No Renaissance whitewashing. The tesserae remained untouched for a millennium.