Entry to the basilica costs nothing, which puts it in a small and valuable category among Rome’s major religious sites.

There is a security check at the door with bag scanning, and a queue forms at busy times, but it moves.

What is ticketed: the museum, the loggia with its mosaics, and guided access to certain areas. Those are modest and optional.

The basilica is one of the four papal major basilicas of Rome, along with St Peter’s, St John Lateran and St Paul Outside the Walls, and it is the only one to have kept its original early Christian structure.

It is an active place of worship, and parts close during services.

Pope Francis chose to be buried here rather than in St Peter’s, in keeping with his long devotion to the basilica, and his tomb is now one of the main reasons visitors come.

It is deliberately simple — a plain marble slab with a single word — and it sits in a side aisle of the basilica.

Access is free and it is part of the ordinary visit. Expect a queue at busy times and expect the atmosphere around it to be devotional rather than touristic.

There is a separate area beneath the basilica holding the tombs of earlier popes, reached by stairs, which many visitors miss.

If you are visiting to pay respects rather than to sightsee, early morning and the quieter hours are considerably more suitable.

The reason this basilica matters art-historically, and the thing most visitors underuse.

The mosaics along the nave date from the fifth century and are among the oldest surviving Christian mosaics anywhere, showing scenes from the Old Testament in a style that is still recognisably late Roman.

The triumphal arch mosaics are from the same period.

The apse mosaic is medieval and shows the coronation of the Virgin in gold ground.

They are high up and the nave is long, so a pair of binoculars or a phone camera zoomed in is genuinely useful. Most people photograph the ceiling and never look at the walls above the columns.

The loggia at the front, ticketed and reached by a short guided visit, holds further mosaics and gives a view over the square.

The gilded coffered ceiling is the thing that stops people in the doorway. According to tradition it was gilded with the first gold brought back from the Americas.

The nave columns are ancient, reused from Roman buildings, which is why they match so precisely.

The floor is Cosmatesque — medieval geometric inlay in coloured stone — and is worth looking down at as well as up.

Two enormous side chapels, the Sistine and the Borghese, are effectively churches in their own right and hold papal tombs.

The basilica also claims a relic of the Holy Crib, displayed in the confessio beneath the high altar.

This is a papal basilica and the dress code is enforced: shoulders and knees covered, for everyone, hats off inside.

There is airport-style security at the entrance with bag scanning. Allow a few minutes, more at peak times.

Large bags may be refused, so travel light.

Silence is expected in the nave, and parts of the basilica close during Mass — which is worth checking if your window is narrow.

Attending a service is free and is the calmest way to be inside the building, though it is worship rather than a visit.

Early morning is quietest and the light through the high windows onto the mosaics is at its best.

Mid-morning to mid-afternoon is the busiest, particularly since the papal tomb became a draw.

Late afternoon thins out again.

The basilica sits near Termini, so it is a natural first or last stop in Rome — an hour here on an arrival afternoon or before a departure train is a good use of otherwise dead time.

Check service times before planning a narrow visit.

September and October are the busiest months here, with May close behind.

January is the quietest, then December and February.

Being indoors and free, this works in any weather and is one of the better wet-day options in Rome.

August is quieter here than at Rome’s outdoor sites, and the cool interior is a genuine relief in the heat.

The basilica is significant in the Christmas liturgical calendar, so December brings both crowds and atmosphere.

Thirty to forty-five minutes for the basilica itself, including the mosaics and the papal tomb.

An hour with the underground papal tombs and time spent looking properly at the nave mosaics.

Add half an hour for the loggia visit if you take it.

Add more if you are attending a service.

It is a short visit that rewards slowing down. The most common mistake is a five-minute walk through, a photograph of the ceiling, and out — which misses everything that makes the building important.

The basilica sits on the Esquiline Hill, about a five to ten minute walk from Roma Termini, which makes it the most convenient major church in the city to reach.

Termini metro station serves both underground lines, and buses stop on the surrounding streets.

From the Colosseum it is about fifteen minutes on foot, and from the Trevi Fountain around twenty.

The surrounding neighbourhood near the station is workaday rather than picturesque, and the usual station-area precautions apply after dark.

San Pietro in Vincoli, with Michelangelo’s Moses, is a ten-minute walk away and is free — a natural pairing.

Good. The basilica has step-free access and the nave is level, which makes it one of the easier major churches in Rome for wheelchairs and strollers.

Accessible toilets are available.

The underground papal tombs are reached by stairs and are not accessible.

The loggia visit involves stairs.

The square outside is level, and the walk from Termini is on pavements rather than the cobbled lanes that make the historic centre difficult.

Seating in the nave is plentiful, which matters more than it sounds after a day of Roman walking.

Worth addressing, because this basilica is consistently described as one of Rome’s most underrated.

It is not in the picturesque centre, it is near the station rather than the tourist quarter, and it competes with St Peter’s for attention.

What it offers that St Peter’s does not: free entry with a short queue, mosaics twelve centuries older than anything in St Peter’s, an original early Christian plan, and — now — the tomb of a pope who chose it deliberately over the Vatican.

Visitors who go consistently rate it among the best things they did in Rome, and frequently say they nearly did not bother.

If you have half an hour near Termini, this is the best use of it in the city.

There is essentially no criticism of this basilica in the reviews. The only recurring note is that people wish they had known about it sooner.

The thin version: put your head in for five minutes on the way to the station, photograph the ceiling, and leave.

The good version: come early, look at the fifth-century mosaics along the nave with your camera zoomed in, walk down to the papal tombs beneath, pay your respects at the tomb of Pope Francis, and give the Cosmatesque floor and the side chapels the attention they deserve.

It is free, it is five minutes from Termini, and it holds older Christian art than anything in the Vatican. Half an hour, done properly.