How long would it take to 'Raise the Alarm' in a medieval city?

Question

I'm writing a story that involves the protagonists opening the gates of a medieval city to allow an attacking army through - and I need to know how long it would be before the city's garrison realizes what is going on and arrives with enough troops to stop them.

Here are some details:

• The gate will probably be defended by around 25 men.
• The protagonists have 50 armed knights and 50 assassins with them.
• Their plan is to sneak up on the watchmen and silently take them out - however, one will escape and go alert the city's garrison.
• The city is massive, based on Volantis from Game of Thrones.

So basically, there will be a brief fight at the gate, and then it will be opened. As soon as they begin to open the gate the escaped soldier will set off to alert other troops as to what is happening.

But: How long would it be before he arrives back with enough troops to stop them - or until someone else realizes what is happening and comes to put a stop to them?

Answer 1

The entire setup is wrong, as in, it just doesn't work. It is good enough for a Hollywood movie or for a fantasy adventure novel, but it makes no sense in a serious setting.

The problem is the attacking army.

Medieval armies were slow. Glacially slow. The city would learn that an army was headed towards it at least weeks if not months in advance. And an army cannot be hidden: it is big ugly thing moving slowly through the country, devastating everything in its path. Once the city learned that an army is coming, it would naturally adopt a defensive stance; hence our modern "state of siege".

So in practice, the city would already be prepared for defense; there would be no need to raise the alarm. The gate would be closed, towers and ramparts would be manned, regular patrols would sweep the approaches. Most likely, the city would also be in diplomatic communication with the attackers!

For example, in 1682 (yes, Early Modern, but still a great example) the Ottoman Empire decided to take Vienna. War was declared in August 1682. They managed to assemble a great army at Adrianople by March 1683. They arrived in Belgrade in May. The 200,000-strong army arrived at Vienna in July. During this time, the Austrians evacuated the city, leaving only a force of 15000 volunteers commanded by Ernst-Rüdiger von Starhemberg, emperor Leopold established a set of alliances and coordinated strategy with king Jan Sobieski of Poland. (Spoiler: the Ottomans failed to take Vienna.)

So in the normal course of things a medieval or early modern army cannot take a city by surprise. To take a city by surprise, some other factor must be in play; for example, it helps if the army is already in the city as supposed allies, or if the people of the city riot, or if the rulers flee and leave the defending forces without commanders. Or maybe decades of neglect have left the walls of the city unmaintained and indefensible. Or maybe the garrison consists of badly paid and untrained mercenaries who couldn't care less whether the city is taken or not.

Now, this doesn't mean that taking a city by surprise is not a worthy plot point. That such a feat is not actually reasonable in actual warfare is immaterial: we read adventure novels to be entertained. So make the timing suitable for your purpose; explain away the incompetence or treason of the defending military commanders; and so on. Basically, make something up, and just take care to avoid glaring impossibilities.

Answer 2

That depends entirely on how much the city expects to be attacked.

If the city was designed to repel an attack then the main barracks would be build in close proximity to the gates, simply shouting or maybe ringing a bell should be enough to raise the alarm and bring defenders running within a matter of minutes.

If the city is mostly at peace there might be no reinforcements ready to go, which would result in a significant delay while defenders don their armour and collect weapons

Answer 3

The problem is that when the city gate is opened there is no need to move any soldiers there. You just roll everyone behind wall number two patiently waiting for the incoming army to fall into your well-crafted fortifications and bottlenecks.

And you just need one person to open the gate: The gate commander. You do it this way: Anywho commander, here is a nice sum of money equal to all the gold you could ever wish. And here's a safe-conduct for you and your men after we seize the city. Just remember to open the gate on the third night of the second month.

Storming the gates is the worst idea of an attack. Gate is designed, crafted and built to be a cool place to what you youngsters call "camping", even when open. You just stay in recess and poke everyone with a pike through small openings.

You tear down the wall, blast it, make excavation but you don't go through the gates.

Answer 4

Let’s assume that the city is well prepared and the guards well trained. It is possible that the events will occur like this:

Alarm

• The escaping guard remembers its training and know exactly what to do: Ring the closest alarm bell! How close is it? You can chose. But maybe if you have one in each church, plus some others to fill the gaps, you could assume 500 meters. So time before ringing the bell:

  • 500 meters at 4 m/s (good running speed with an armor, adrenaline probably helped) => 2min and 10 sec more or less
  • Add one minute to climb the bell tower
  • The bell is ringing about 3 minutes and a few seconds after the attack. You can make it earlier or later by moving the bell closer or further

• Sound of the bell travelling to the guard house: you can neglect it :)

Response to alarm

• Once the reserve soldiers hear the bell, they will put helmets on, grab their swords and run toward the bell. (They don’t know what is happening, neither which door is under attack.) Again, we don’t know how far this might be. Let’s assume 1 kilometre, you can change this distance to make it faster or slower.
  • If they were not sleeping, but rather in a “ready for action” mode: grab helmets, swords ang go! 1 minute.
  • 1000 meters at 3.5 m/s (they don’t have adrenaline, they have to run for a longer distance, hence are slower): Nearly 5 minutes.

Planning defence

• At the bell the guard explain them what’s happening, they decide of which plan to use (they are trained, they have plans ready for many situations, they just need to find the one that fit the best to this particular situation). Let’s count 30 seconds.
• They run to the door. Again 500m, 3.5 m/s because they want to be cautious when getting close. 2 minutes and 20 seconds.
• In total 1mn + 5mn + 30s + 2mn 20s = About 9 minutes.

Total

If we sum it all, we have nearly 12 minutes between the attack and the guards arriving at the door.

Tricks

A few tricks might make it quicker:

• The guard, after ringing the bell could run toward the incoming soldiers to lead them directly to the gate
• Some kind of watchman could stay close to the bell, so that the soldier could yell at him when he gets close enough and so avoid climbing the stairs
• The bell signal could convey information about which door is under attack, so the soldiers would go there directly. (one Booong: door one, ...)

In summary: you can make it much longer or much shorter. But around ten minutes seems reasonable in a big city, especially if the attacking army did choose on purpose a door which is far from the bells and the guard house.

Final note: This answer is more of a hint on how to calculate it, so put your own numbers in it if you have some. Mines are just guesses.