Cerca de la muralla había una plaza tranquila desde la que se veía la sierra al fondo.

Because haber is commonly used to say that something existed or was there: había una plaza = there was a square.

Estaba would describe the location or state of something already introduced:

• Había una plaza cerca de la muralla = There was a square near the wall.
• La plaza estaba cerca de la muralla = The square was near the wall.

So había introduces the square as part of the scene.

Cerca de means near or close to.

In Spanish, cerca normally needs de before the thing it is near:

• cerca de la muralla = near the wall
• cerca de casa = near home

So you should learn cerca de as a fixed expression.

Not exactly.

• muro = wall in a general sense
• muralla = a large defensive wall, usually around a town or fortress

So la muralla suggests a city wall or fortification, not just any ordinary wall.

In Spain, plaza usually means a public square, not a shopping mall.

So una plaza tranquila means a quiet square or a peaceful town square.

Also, tranquila agrees with plaza, which is feminine singular:

• una plaza tranquila
• un lugar tranquilo

The imperfect is often used for background description in the past.

This sentence is painting a scene:

• había una plaza tranquila = there was a quiet square
• se veía la sierra al fondo = you could see the mountain range in the distance

These are not presented as completed events, but as part of the setting. That is why the imperfect fits well.

Desde la que means from which.

It refers back to la plaza:

• una plaza tranquila desde la que...
• literally: a quiet square from which...

Why la que?

• que is the relative pronoun
• la matches plaza, which is feminine singular
• desde must stay because the idea is from the square

So:

• la plaza → desde la que
• el mirador → desde el que
• las ventanas → desde las que

Yes, in many contexts you could say:

• ...una plaza tranquila desde donde se veía la sierra al fondo.

That is also natural and often feels a bit more conversational.

However, desde la que is slightly more explicit and a bit more formal or literary. Both are correct here.

Here se veía gives an impersonal sense, similar to:

• one could see
• the mountain range could be seen

So:

• desde la que se veía la sierra = from which the mountain range could be seen

If you said veía, you would normally need a subject:

• yo veía
• él veía
• la gente veía

With se veía, the sentence avoids naming who was doing the seeing and focuses on the view itself.

No. Here la sierra means mountain range or highlands.

Spanish sierra can mean:

• saw as a tool
• mountain range

In this sentence, the landscape meaning is clearly intended:

• se veía la sierra al fondo = the mountain range could be seen in the distance

Al fondo means in the background, in the distance, or farther back.

It is made from a + el = al:

• al fondo

In this sentence, it means the mountain range was visible far away, in the background of the scene.

Spanish often moves place expressions to the front to set the scene first.

So:

• Cerca de la muralla había una plaza tranquila...

This sounds natural and descriptive, like beginning with the location and then introducing what was there.

A more neutral order would also be possible:

• Había una plaza tranquila cerca de la muralla...

But the original word order feels more literary and scene-setting.

Yes, and in this sentence could see is often the best translation.

Because the sentence describes what was visible from the square, se veía often has the sense of was visible or could be seen, not necessarily a single act of seeing:

• desde la que se veía la sierra al fondo = from which you could see the mountain range in the distance

So could see or could be seen usually captures the idea better than a simple saw.