Ancient Greek automatic doors

Here’s a surprising discovery: Ancient Greeks had automatic doors.

Alexandria in the 1st Century CE had at least one set of doors that opened automatically. The mathematician and engineer Heron of Alexandria developed a hydraulic system to open and close temple doors.

Greek temples had fires burning at the altar. Heron suspended a brass pot under the fire, half filled with water. This brass pot was connected to a few containers that acted as weights attached to a pulley system. When a priest lit the fire, the air inside the brass pot would expand, forcing the water into the containers. These containers descended as they were filled, dragging down the pulley ropes and opening the doors.

The doors were opened once a day as worshippers arrived at the temple. The system would take several hours from a priest lighting the fire to the doors opening. Its main purpose was to create a sense of mysticism and suggest divine power.

Heron described the mechanism, alongside a number of pneumatic and hydraulic inventions, in Pneumatika (Schmidt XXXVIII) and named it ‘Machine Number 37’. Heron’s text suggests he built a similar mechanism of automatic doors at Alexandria’s city gates.

A bit of background: in the 1st Century CE, Alexandria had been taken over by the expanding Roman Empire, but its Greek population and culture remained largely unchanged. People were still free to worship their original Greek gods and new Greek temples were still being built.

Modern automatic doors, powered by electricity and triggered by sensors recognising people approaching, were first invented in 1931.