Zhang Mengyao had retaken Lisbon from the mercenary. There was no more fight after the initial of a hundred mercenaries just like Lu An told them. A hundred mercenaries were supposed to guard the portal and report if the Tang Empire went through. However, the mercenaries took the matter by themselves and got killed before they could report.
"We actually need people who know this place. We can use our advantage and strike from the back while they are unaware we have taken Lisbon from them," Zhang Mengyao's plan was quite simple and straightforward, but the execution mattered.
The issue was that they lacked the knowledge of the area for Europe. They needed someone to lead them to move from one city to another. If they moved recklessly in a big number, The World Government might discover their movement.