Before Eragon quite knew where he was, the trees became more numerous and then thickened into a wall.

The trees thickened quickly once he was inside the forest.

The houses separated as the trees thickened and soon there were few to be seen.

The countryside changed its look as the trees thickened and the forests grew more dense.

The trees ahead thickened, trunks tightening in a dark wall, limbs closing out the night sky.

The sky was purple and the trees were thickening with shadows.

I followed a steep sandy path that gradually became covered with pine needles as the trees thickened around me.

As the trees thickened, the ground roughened, he followed the water.

The trees and liana thickened, as did the darkness.

On the fourth side the trees and shrubs slowly thickened, until a few hundred feet away they became a solid mass of greenery.