The big guns have arrived in the Scottish Cup, the start of a possible journey to Hampden Park but also one with plenty of potential for embarrassment at the hands of lesser foes.

This season, the Scottish Cup fourth round stretches over four days as the 12 Scottish Premiership sides join those from the lower leagues who have progressed through the earlier rounds.

Here are some of the key ties as we sort out who will be in Monday's draw for the last 16.

The luck, or bad luck, of the draw means not too many lower league sides have home ties that immediately suggest a cup shock could be on the cards, but four still jump out.

Brechin City v Heart of Midlothian (Live on BBC Scotland and online, Fri 19:45 GMT)

First up is Friday night's game live on the BBC Scotland television channel as Highland League leaders Brechin City entertain top-flight Hearts.

Considering Brechin were in the senior leagues until relegation in 2021, it is perhaps surprising that the sides have only met in three previous cup ties, with Hearts prevailing each time, once after a replay.

The current side led by former Hibs midfielder Patrick Cregg have struggled a bit to reach the fourth round for the first time since 2018, when they were in the Championship.

Two single-goal home wins - over Newtongrange Star, of the East of Scotland League, and Highland rivals Huntly - took Brechin through the first two rounds before needed extra time before overcoming Lowland League hosts Cowdenbeath 4-1.

However, they are in pole position to win the Highland League for the second time, leading by two points from Brora Rangers, and have gone 11 games without defeat at home.

Eight-time cup winners Hearts will arrive in better mood than when the draw was made, Neil Critchley's side having lifted themselves off the bottom of the Premiership after four games without defeat.

However, having struggled to beat League 2 side Spartans 2-1 away from home at the same stage last season, the Edinburgh side will be aware of the dangers.

Elgin City v Aberdeen (Live commentary on BBC Radio Scotland and online, Sat 15:00)

So too fellow beaten semi-finalists Aberdeen, who travel to face Elgin City in crisis mode after 12 games without a win and with their stunning unbeaten start to the season under new manager Jimmy Thelin long forgotten.

The sides have only met twice before, both in the cup, with Aberdeen winning 6-1 in Elgin in 1938 and 5-0 at home in 1971 - both while City were still in the Highland League.

However, the Dons' worst-ever cup exit, to sixth-tier Darvel two years ago, is still fresh in the memory and the side sitting third in League 2 will have learned from their 5-0 League Cup thrashing in the opening game of the season against top-flight Hibs.

Allan Hale's side have only lost once at home in 12 games since.

Queen of the South v St Mirren (Live updates on BBC Radio Scotland and online, Sat 15:00)

Having suffered four straight defeats, Stephen Robinson's St Mirren are another Premiership side looking vulnerable.

They knocked Queen of the South out at the same stage last season - but only by a single Alex Gogic goal at home.

This time, the side sitting sixth in League 1, and now managed by Peter Murphy, have home advantage having not lost at Palmerston in five games, albeit their last defeat was a particularly sore one - 5-1 by Kelty Hearts.

However, the Buddies have won on their latest nine meetings, winning five in Dumfries since their last defeat there in February 2016, and will be favourites to prevent Queens reaching the last 16 for the first time since 2019.

Broxburn Athletic v Ayr United (Live updates on BBC Radio Scotland and online, Sat 15:00)

Broxburn Athletic have already caused a mini-upset in this season's cup, having ousted League 2 strugglers Stranraer 2-1 away from home.

Hosting an Ayr United side currently unbeaten in five under Scott Brown, four of them wins, and having narrowed the gap with Championship leaders Falkirk to two points in midweek, is a much tougher ask.

However, the side led by former Dundee and Partick Thistle defender Steve Pittman are giving a good account of themselves in their Lowland League debut, sitting sixth after winning last season's East of Scotland League.

Monday's Dundee derby grabbed the headlines when the draw was made, but there are two other all-Premiership ties before the city rivals do battle for the final spot in the last 16.

Celtic v Kilmarnock (Live commentary on BBC Radio Scotland and online, Sat 17:30)

Cup holders Celtic will be favourites to progress when they entertain Kilmarnock on Saturday considering Brendan Rodgers' runaway league leaders have not lost in 28 home games - 16 of them this season.

If ninth-placed Kilmarnock are to emulate Hearts' win at Celtic Park in December 2023, they will have to do what they have failed to do in their latest three meetings - all defeats with the loss of 11 goals - and that is score one of their own.

They did draw 1-1 at Celtic Park in the game before that - and won 2-1 at Rugby Park immediately before that too - so Derek McInnes' side know it is possible despite the odds but will have to turn around form that has led to one win and three blank sheets in their latest four outings.

St Johnstone v Motherwell (Live updates on BBC Radio Scotland and online, Sat 15:00)

Either St Johnstone, aiming to reach the last 16 for the first time since lifting the trophy in 2021, or Motherwell will end their dismal recent run on Saturday.

Saints have fallen nine points adrift at the bottom of the Premiership with no wins in nine outings, seven of them losses, under new manager Simo Valakari and seem destined for relegation.

Visitors Motherwell, suffering a spate of injuries, have themselves just one victory in seven, but Stuart Kettlewell's side have won 2-1 home and away against the Perth side already this season and have not lost in five visits to McDiarmid Park.

Dundee v Dundee United (Live commentary on BBC Radio Scotland and online, Mon 20:00)

In contrast, the other game in Tayside brings together city rivals on a bit of a high.

Dundee are 10 points and four places below third-top United after only two wins in eight outings, but Tony Docherty's side have recovered from a poor spell and are not only unbeaten in three, but the latest two have been creditable draws with the top two sides - Rangers and Celtic.

After a 1-0 win away to St Mirren last time out, Jim Goodwin's visitors have only lost twice in seven and will be looking to repeat their 2-1 league win at Dens Park just over a fortnight ago.

Indeed, United have not lost on the other side of Tannadice Street in eight visits since August 2017.

For some, barring an upset of historical proportions, progress to the cup fourth round is just all about a big pay day and the romance of the cup.

Rangers v Fraserburgh (Live on BBC One Scotland, BBC Radio Scotland and online, Sun 14:15)

Philippe Clement has survived calls from some fan groups for his sacking after Rangers fell so far behind reigning champions Celtic in the league race, but the Belgian would surely never recover should the side sitting ninth in the Highland League be the first Scottish team to win at Ibrox this season.

Mark Cowie's Fraserburgh are themselves unbeaten in 11 outings as they prepare to play in front of BBC One Scotland television cameras, but only three of them were away from home and all those were draws.

Rangers, last season's beaten finalists, were visitors to Fraserburgh almost exactly seven years ago, leaving with a 3-0 win, but the part-timers' chairman, Michael Murray, says it is the size of the likely crowd at Ibrox that will be a financial game-changer for his club this time.

They did beat League 1 side Annan Athletic in the last round, but virtually nobody expects a repeat of 1959, when the Highland side beat Dundee, then third in the top flight, 1-0 in one of the greatest cup upsets.

Hibernian v Clydebank (Live updates on BBC Radio Scotland and online, Sat 15:00)

In a previous incarnation, Clydebank were a top-flight club, but only now is the new one beginning to emerge from the Airdrie United takeover that led to their demise 22 years ago and they currently lead the West of Scotland Premier League.

Darvel made the sixth tier famous with their cup upset over Aberdeen a couple of years ago and Gordon Moffat's Bankies might have seen a glimmer of hope when the draw was made with Hibs in the Premiership relegation zone.

However, David Gray's side have since gone seven games unbeaten, winning five of them, to move up into the Premiership's top six, while this will be Clydebank's first competitive game since a 1-1 draw away to Glenafton Athletic on 14 December.

Little chance then of a repeat of Hibs' last meeting with the old Clydebank, when it finished 1-1 at Easter Road before the Leith side won 3-0 in the replay to progress 25 years ago.