Across as a preposition and an adverb
Across can be used as a preposition or an adverb. When used as a preposition, it is followed
by a noun.
We walked across the desert. (Here the noun the desert acts as the object of the preposition
across.)
Across means from one side to the other.
She walked across the road. (= She walked from one side of the road to the other side.)
Across can be used to talk about movement from one place, space or line to the other.
The airplane flying across the Atlantic when it developed engine trouble.
They are building a bridge across the river. (= The bridge will extend from one side of the
river to the other side.)
Across can also be used to show the width of something.
The river is only a few meters across in some places.
Across can show position. It means on the opposite side of a road, river, line etc.
There is a petrol pump just across the road. (= The petrol pump is on the opposite side of the
road.)
The people across the border are moving. (= The people on the opposite side of the border
are moving.)
Across can also be used to show position in many parts of an area or country.
They have several offices across Europe. (= They have several offices in many parts of
Europe.)
Across can also be used for saying that something affects a large part of your body.
Suddenly he felt a sharp pain across his chest.
Across is also used for saying that something spreads until it covers the whole of a particular
area.
A warm smile spread across her face.
When used as an adverb, across is not followed by a noun.
She hurried across to greet us. (Here the adverb across modifies the verb hurried.)