A relay computer

In the original long-form version of Rome's Revolution, we got a better understanding of what the Ibbrassati were trying to accomplish in their secret enclave in the north woods. Fridone was leading Rei out of the cave, on their way back to the fallen Ark when they stopped in the "work cave" where Fridone showed off what they had accomplished.

     “This is our workroom,” Fridone said. He pointed to one corner. “Over there, we are working on building a computer.”
     “Can I see?” Rei asked.
     “Of course.” Fridone led Rei over to the work area indicated. The people there leaned away so that Rei could see. There was a large flat surface, a table. Resting on it was a cabinet which was filled with blinking lights. The front plates of the cabinet had knobs and dials and banks of switches. It looked straight out a bad movie from the 1950s.
     “How do you build a computer?” Rei asked. “How do you power it?”
     “It is a mechanical computer,” said Fridone. “It uses relays. It can perform small tasks but we are using it mainly to design a more powerful computer.” Fridone motioned for Rei to come around to the rear of the table. He stooped down. Rei stooped down with him.
     “We have constructed batteries out of dissimilar metals in an acid solution,” he said, pointing to the wooden buckets stacked below. “None of them are very efficient but we use many, many of them to create the power we need.”
     Rei stood up. “I certainly can help you with that part. Every one of our sarcophagi have two power rods. You can get rid of these things and have real power, infinite power. And we have a nav-computer. That should help.”

It was only because Rei was an engineer that he even knew what a relay-based computer was.