Across, over or through?

We use across as a preposition (prep) and an adverb (adv). Across means on the other side of something, or from one side to the other of something which has sides or limits such as a city, road or river:

We took a boat [PREP]across the river.

[PREP]Across the room, she could see some old friends. She got up and went to join them.

My neighbour came [ADV]across to see me this morning to complain about our cat.

The road was so busy that we found it difficult to get [ADV]across.

We also use across when something touches or stretches from one side to another:

The Ponte Vecchio is a beautiful old bridge across the river Arno in Florence.

She divided the page by drawing a red line across it. Then she cut it in two.

Especially in American English, across from is used to refer to people or objects being ‘opposite’ or ‘on the other side’:

The pharmacy is across from the Town Hall.

Helen’s office is just across from mine.

We use across to emphasise that something is happening at the same time in many places, e.g. within an organisation, a city or a country:

She’s opened coffee shops across the city and they’re very successful.

Across the country, people are coming out to vote for a new president.

We also use across to refer to the width or diagonal measurement of something:

The size of a television screen is measured from the higher corner of one side to the lower corner of the other side, that is, from one corner across to the opposite corner.

Across comes after measurements when we talk about diameter or width:

The building is 157 metres long, 92 metres across and the façade is 68 metres wide.

We use over as a preposition and an adverb to refer to something at a higher position than something else, sometimes involving movement from one side to another:

From the castle tower, you can see [PREP]over the whole city.

We toasted marshmallows [PREP]over the fire.

We drove high up [PREP]over the mountains on a narrow dangerous road.

Suddenly a plane flew [ADV]over and dropped hundreds of leaflets.

Come over often means to come to the speaker’s home:

You must come [ADV]over and have dinner with us some time.

Especially when we use them as adverbs, over can mean the same as across:

We walked over to the shop. (or We walked across to the shop – the shop is on the other side of the road)

I was going across to say hello when I realised that I couldn’t remember his name. (or I was going over to say … meaning ‘to the other side of the street or room’)

• When moving from one side to another while surrounded by something, we use through not across:

We cycled through a number of small villages.

Not: We cycled across a number of small villages.

• When we talk about something extending or moving from one side to another, we use across not on:

The papers were spread across the table.

Not: The papers were spread on the table.

• We don’t use through when we’re talking about periods of time from start to finish and we mention a specific number of days, weeks, etc:

We haven’t seen each other much over the last four years.

Not: We haven’t seen each other much through the last four years.