The Mediaeval concept of the universe stood for about two thousand years as the principle of how the universe functioned. It is rooted in the physics of Aristotle and astronomy of Ptolemy. The basic idea of this is that the universe is a sphere with the earth at the centre, with the whole thing divided into 2 main regions. These are the sub- and supralunar - meaning that which is between the moon and earth (the sublunar) and that which is between the moon and the outermost circumference of the universe, the supralunar.
The supralunar is comprised of the moon, planets and sun, which revolve around the earth in fixed circular orbits. These entities were regarded as more perfect than those in the sublunar as they were thought to be immutable - immune to corruption and decay - which, in the scheme of mediaeval thought, is better as it is closer to God - ie more perfect.
On the other hand, in the sublunar there is more than just perfect circular motion: there is death and decline, locomotion, and general change. Instead of circular motion, there is rectilinear motion in which each object moves towards what Aristotle defined as its 'natural place': objects down towards the ground, fire upwards to the sky. This is not as admirable as the supralunar.
It was the difference between the type of changes that occurred in each region that was the defining difference: the two regions were defined as having totally different systems of physics. What prevailed through both systems however was the idea of Teleology. This concept states that everything has a purpose, and had it not a purpose, it could not exist (When Galileo claimed to have seen Jupiter's moons through his telescope, his claim was rejected as these moons would serve no purpose). According to the mediaeval ideas, the universe was like an organism, with each part striving for a common goal and purpose. During the 17th century, science made headway, and this conception of the universe was dramatically broken down and replaced by ideas from which our conception stands today.