2 Samuel 20:14 Sheba passed through all the tribes of Israel to Abel Beth Maakah and through the entire region of the Bikrites,(b) who gathered together and followed him. 15 All the troops with Joab came and besieged Sheba in Abel Beth Maakah. They built a siege ramp up to the city, and it stood against the outer fortifications. While they were battering the wall to bring it down, 16 a wise woman called from the city, “Listen! Listen! Tell Joab to come here so I can speak to him.” 17 He went toward her, and she asked, “Are you Joab?”

“I am,” he answered.

She said, “Listen to what your servant has to say.”

“I’m listening,” he said.

18 She continued, “Long ago they used to say, ‘Get your answer at Abel,’ and that settled it. 19 We are the peaceful and faithful in Israel. You are trying to destroy a city that is a mother in Israel. Why do you want to swallow up the Lord’s inheritance?”

20 “Far be it from me!” Joab replied, “Far be it from me to swallow up or destroy! 21 That is not the case. A man named Sheba son of Bikri, from the hill country of Ephraim, has lifted up his hand against the king, against David. Hand over this one man, and I’ll withdraw from the city.”

The woman said to Joab, “His head will be thrown to you from the wall.”

22 Then the woman went to all the people with her wise advice, and they cut off the head of Sheba son of Bikri and threw it to Joab. So he sounded the trumpet, and his men dispersed from the city, each returning to his home. And Joab went back to the king in Jerusalem.

b. 2 Samuel 20:14 See Septuagint and Vulgate; Hebrew Berites.

Did you see that... they built a "siege ramp".

I'm starting with Bibletrack.org this morning.

In pursuit of Sheba and his army, they locate him in a walled city named Abel in northern Israel. As they begin to besiege the city and tear down the walls, a woman of the city propositions Joab with her solution, "How 'bout we just throw Sheba's head out to you, and you go home?" "Good deal!" replies Joab. Soon afterward, here comes Sheba's head as promised, and everybody goes home - rebellion ended. David's back, and so is Joab! And Amasa? He's just lying dead in a field somewhere; it's not wise to cross Joab.

Incidentally, the Cherethites and Pelethites in verse 23 were likely a couple of Philistine tribes in Southern Israel who were loyal to David. Many scholars think they were King David's guards. We are told that it was common practice among monarchs during this period to have a guard of foreign mercenaries.

Bible.org offers this.

Joab and his forces finally track down Sheba at Abel Beth-maacah. When they hear that Sheba has sought refuge in this fortified city, they put the city under siege. The people inside the city do not even know why their city is under attack, but they look on with fear as Joab and his men begin to dismantle the city piece by piece. It is only a matter of time before Joab breaks through into the city. At that point, not only will the city be destroyed, but many people will likely die in the confrontation.

A wise woman sizes up the situation and takes the initiative. She goes to the wall, calls down, and asks to speak to Joab. He comes near, and she recounts to him how this city has been highly esteemed as a source of wisdom and counsel. It is a place known for ending disputes. Why then would Joab want to destroy such a place? She goes on to tell Joab that she is among those in the city who are peaceable and faithful in Israel. They have done nothing to deserve what Joab is dishing out. This is a part of the “inheritance of the Lord.” Does Joab really wish to be responsible for destroying it?

Joab assures the woman that he does not wish to destroy the city. He then informs her why the city is being besieged. They are seeking but one person, Sheba the son of Bichri, who is guilty of rebellion against King David. If the woman will arrange to have this man handed over to them, they will go their way in peace. The woman assures Joab that Sheba's head will be thrown over the wall to him. The woman then convinces the people of the city to execute Sheba, and his head is thrown down to Joab and his army. With this, Joab blows the trumpet, indicating the cessation of hostilities. Joab then returns to Jerusalem and King David.

Still nothing about that siege wall. I found this under Biblestudytools.com after a google search.

Following upon this was the mound (colelah), or earthworks, built up to the height of the walls, so as to command the streets of the city, and strike terror into the besieged. From the mound thus erected the besiegers were able to batter the upper and weaker part of the city wall (2 Samuel 20:15; Isaiah 37:33; Jeremiah 6:6; Ezekiel 4:2; Daniel 11:15; Lamentations 4:18). If, however, the town, or fortress, was built upon an eminence, an inclined plane reaching to the height of the eminence might be formed of earth or stones, or trees, and the besiegers would be able to bring their engines to the foot of the walls. This road was even covered with bricks, forming a kind of paved way, up which the ponderous machines could be drawn without difficulty. To such roads there are references in Scripture (Job 19:12; Isaiah 29:3, "siege works"; compare Layard, Nineveh and Its Remains, II, 366 f). In the case of Tyre this mound, or way of approach, was a dam thrown across the narrow strait to obtain access to the walls (Ezekiel 26:8). Very often, too, there was a trench, sometimes filled with water, at the foot of the wall, which had to be dealt with previous to an assault.

So... Sheba did make it to a fortified city. Apparently those relentless soldiers under Joab would have hauled up enough rocks or dirt to build a wall mound up to the top of one of the walls. The fortified cities had towers and archers at the top of the walls and they would shoot arrows at the troops the whole time they were building the mound. There would be major losses on both sides while the siege mound was being built. Then... when the thing was finished.... Joab and his troops would have simply walked over the top of the wall of the city... down into the town.... killing everyone in sight until they found Sheba.

This woman... unnamed woman.... saved hundreds, maybe thousands of lives.