Once we define what we want and build the smallest increment, we want to integrate it into our system as soon as possible so that we can see it working and get a true measure of our progress.
Continuous integration is at the very heart of every Agile project and so I wanted to introduce it as early as possible. To me, it's the third central pillar of agile software development. Continuous integration means having a fully automated build that not only compiles and runs a system but also fully tests it without the need for any human intervention.