Matthew Poole and continuators on Ezekiel 40:18

18 And the pavement by the side of the gates, over against the length of the gates was the lower pavement.

That mentioned verse 17.

That part which lay on each side of the gate, and from thence spread it self towards the chambers, leaving a space of pavement of equal breadth with the porch, or gate in the middle.

This length was measured fifty cubits ver. 15. from the outside of the first wall to the outside of the inmost wall of the gate and porch, from which, on a pavement somewhat raised, as in other stately walks, this went on to the next gate of the next Court.

The side pavement was laid somewhat lower then this middle pavement, not onely for state, but for the more convenient keeping it clean, so the middle pavement rose with a little convex surface, and the edges sunk with a little declivity.