After arriving on Earth, the Espheni Queen turned the Lincoln Memorial into her base of operations. As part of this, to protect it, she had a powerful defensive wall built around the Mall area so that the humans couldn't reach her without suffering heavy casualties. It is speculated that the sewers would be set up with traps to prevent anyone approaching from that way, but the service tunnels, one of which has an exit near the Memorial, would be safe. Indeed, apart from putting Espheni eggs in the tunnels, there were no guards.
Following the discovery of the Shadow Plane device, Ben Mason was able to connect to it with his spikes and learn of the existence of the Espheni Queen. The image he saw showed the Overlords bowing before the Queen at a set of stairs. This was likely meant to represent the Lincoln Memorial where the Queen's base was located.
After the discovery of the existence of the Espheni Queen, Ben began using the Shadow Plane to try to locate exactly where the Queen was in Washington, D.C. Amongst other things, he discovered that she was calling all the Espheni to gather before her, but was initially unable to find her exact location. Finally, Ben discovered a clue, "at the foot of the giant" and the fact that the Alexis Glass-Mason was actually an Espheni clone. After the clone was killed with the Dornia bioweapon, but not before revealing crucial information about the Espheni Queen and her plans, the 2nd Mass set out to try to figure out Ben's clue and locate exactly where the Espheni Queen is in Washington, D.C. Finally, after staring at a map of the city, Tom Mason noticed the Lincoln Memorial and realized that it was the one place in Washington, D.C. that matched the clue. With a definitive target for their attack, the 2nd Mass and the 14th Virginia prepared to set out the next morning for the Lincoln Memorial.
Following a Black Hornet attack on their base, the two militias were delayed in leaving until the next morning when they got a radio message informing them that the Lincoln Memorial and the area surrounding it were protected by a powerful defensive wall, presumably built by Skitterized humans. Overlords, Skitters, Black Hornets, & Skitterized Humans patrol the wall & defend the grounds from the resistance to protect the Queen. Realizing that they couldn't safely breach the wall, an alternate plan was made to have the other militias attack the wall as a distraction while Tom and Colonel Daniel Weaver lead a strike team through the city's service tunnels to reach the Lincoln Memorial and attack the Queen directly. During the following assault on the city, Lieutenant Demarcus Wolf was able to lead the strike team through the tunnels towards the nearest exit to the Lincoln Memorial on the Mall, using his knowledge of the tunnels from growing up in Washington, D.C. as the son of a high-ranking military official. After an Espheni hatchling attack separates Tom from the rest of the team, he continues on alone while the rest of the team tries to find their own way out. Emerging from the tunnels, Tom finds himself in front of the ruins of the Lincoln Memorial which are undefended thanks to the effective distraction of the attack on the wall. In the ruins, Tom finally comes face to face with the Espheni Queen who pins him to a wall with some webbing and explains the history of the Espheni and Earth and what led up to the Invasion of Earth. As the Queen starts to drain his blood, Tom infects himself with the Dornia bioweapon which passes through his blood and into the Queen. The Queen is killed and the virus passes through her into her species, wiping out the Espheni. Seeing the Espheni and their creations explode all over the Mall and the sky, Tom collapses on the steps on the Memorial. Shortly after sunrise, Ben finds him there and leads him back to the rest of the strike team where Tom's mortally wounded wife has died of a shrapnel injury.
Months later, a now-united humanity gathers at the rebuilt Lincoln Memorial to elect a new leader for the entire species. Thousands of people gather through the Mall to hear Tom Mason's speech and the Volm are also in attendance.