The castle of Lamia occupies the city's fortified acropolis, a hill used for defense from antiquity. Its walls preserve masonry from several periods, reflecting repeated repair rather than a single foundation. The site overlooked routes between central and northern Greece and the plain of the Spercheios. Lamia became prominent during the Lamian War of 323–322 BCE, when a coalition led by Athens challenged Macedonian power after the death of Alexander the Great. The Macedonian regent Antipater took refuge in the fortified city while allied Greek forces besieged him.

During the siege the Athenian commander Leosthenes was killed, and the coalition eventually lost momentum. Reinforcements allowed Antipater to escape the immediate crisis, and Macedonian victories ended the war. Although the precise form of the ancient defenses changed over time, the episode established Lamia's strategic place in the struggle over the post-Alexander Greek world. Roman and early Christian occupation followed. Repairs to gates, towers, and curtain walls reused earlier stone, making the hill a physical record of political continuity even when rulers and urban institutions changed.

In the Middle Ages the acropolis remained important under Byzantine and western rulers. Frankish and Catalan forces controlled Lamia at different times during the thirteenth and fourteenth centuries, when the town was often known in western sources as Zeitounion or related forms. The fortress guarded a contested corridor linking Thessaly, Boeotia, and the coast. New rulers modified existing defenses rather than replacing them completely. Churches, cisterns, houses, and military quarters occupied the summit according to the needs of successive garrisons and communities.

The Ottomans took control in the fifteenth century and retained Lamia until the formation of the modern Greek state in the nineteenth. The castle served administrative and military functions, with repairs responding to artillery and local security. After Lamia became part of Greece in 1833, the summit continued in state use. Barracks and other military installations occupied the enclosure during the reign of King Otto and into the twentieth century, including periods of wartime activity. This long occupation helped preserve the strategic site while also obscuring or disturbing earlier remains.

The Archaeological Museum of Lamia opened within the restored barracks in 1994, bringing finds from prehistoric through Roman times into the castle itself. Conservation of the fortifications and museum buildings now presents the hill as both monument and repository. The castle's significance reaches beyond one famous battle: ancient masonry, medieval rebuilding, Ottoman occupation, modern barracks, and archaeological display all occupy the same acropolis. Lamia demonstrates why commanding places were rarely abandoned entirely and why their walls must be read as cumulative structures shaped by changing states, technologies, and civic identities.