There was a gun there that had been part of the town's port defences in the Spanish Civil War. The notice alongside said that particular gun had been involved in a duel between the shore batteries on opposite sides of the harbour in March 1939 (the end of the Spanish Civil War) and that it had sunk a ship called Castillo de Olite on the morning of 7 March killing 1476 people and injuring 342 - the largest loss of life in any Spanish Naval engagement. I didn't understand; why were the shore batteries shooting at each other? Cartagena had remained loyal to the Republican (Socialist) side right to the bitter end so far as I knew. So I checked. It seems that the various Republican factions within the city, Communists, Anarchists and what not, got to squabbling as General Franco's troops closed in on them and as the war moved towards its inevitable conclusion. The Nationalists ("Fascists") who'd been in the city all the time but keeping a low profile used the opportunity to come out with guns blazing. They took the city's radio station and the guns on one side of the harbour. That's why the guns were shooting at each other. Hearing on the radio that the city had been taken by the Fascists Franco sent a troop ship, that ship was the Castillo de Olite, but by now his side had been beaten back and the Republicans were back in charge of the whole city. So when the ship came into port - BOOM!
Oh, and the museum had a whole room full of little models of tanks, armoured cars and the like. The room was called something like the Guinness Room because the museum houses the largest private collection of models of military vehicles and equipment in the World - they have the certificate from the Guinness Book of Records to prove it. 1579 items if you're interested.
There's a Roman Theatre in Cartagena. It's probably the biggest tourist draw in town but they didn't even know it was there till the late 1980s because right from the Byzantine period people have been building on top of it. Cartagena, under various names, has been a big and important town for a long time - Phoenicians, Romans, Hannibal and his elephants and so on. Somewhere in the exhibition about the history of the theatre it mentioned that Cartagena fell on hard times in the 1400s. So hard that there were only 800 people left in the town. Crikey.