The Romans were good at building and engineering, but not so good at inventing machines. There were always plenty of slaves to do the nasty jobs, so nobody bothered to think up machines that could take their place. An example of this was central heating which involved lots of effort from Roman slaves. Public baths and rich people's houses all had central heating.

Central heating worked because hot air moved through spaces under the floors and up the walls. The space was made by building the floor on top of piles of tile or stone and the walls between rooms were really two walls with a gap between them. This was called a hypocaust. The hot air came from a furnace and it was the slaves' job to keep the furnace well stoked up so that the central heating worked.

Although they did not invent arches in buildings, the Romans were the first people to use them to construct bigger, wider buildings without having lots of rows of pillars to hold the roof up.

Aqueducts were made from a line of arches joined together, with a channel on the top to carry water. The Romans used them to supply towns with water.

The arches would be higher or lower as the aqueduct covered rough ground but it would always have a slight slope towards the town so that the water could run downhill.

The Romans also invented the best drains in the world. Towns and forts had underground drains to take away dirty water and sewage. They were flushed through with water from the baths so that they didn't get too smelly.

Fresh clean water and sewers are important because without them people often catch diseases from drinking dirty water or from sewage left around the streets and houses.