When King Fernando got news that a great fleet was being prepared in Castile to attack Lisbon, upon his departure from the city he left in command of its defence Gonçalo Mendes de Vasconcelos and his sons, together with a number of others. While he was thus acting as officer of the marches in Lisbon, there arrived on 7 March 1382 eighty sailships, including naos and barques, which had been fitted out in Vizcaya and in other seaports. Aboard them were many gallant knights, squires, men-at-arms and many foot soldiers bearing shields who were known as the bumpkins. They had that name because they came from the mountains of Vizcaya and were barefoot and ill equipped.

When the fleet anchored before the city, they launched all the ships’ rowing boats, armed and fitted with protective shields, and all proceeded together to the Monastery of Santa Clara, about a crossbow shot's distance beyond the city. The people inside the city wanted to come out, in order to prevent the ground there being taken, but Gonçalo Mendes, the governor, forbade anyone to go outside the city, because the king had given him the specific charge of defending it well. Nevertheless, a few people went out against his will, but some of them were wounded, and Gomes Lourenço Fariseu, at that time a judge in the city, was killed. The Castilians took the ground without encountering anyone else defending it.

A few days later, the men in the fleet, noticing how those in the city did not come out to confront them, furnished all their rowing boats once again with armed men and crossbowmen. They all landed between the city and Santos, which is about two bowshots’ distance further down towards the mouth of the river. But Gonçalo Mendes continued to restrain those in the city, saying they should not go out, because the king had ordered him only to guard the city, and they were to follow orders.

When the Vizcayans saw that nobody came out to challenge them, they returned to their boats and so to the fleet. From then on, they became bolder about sallying forth, both on the Lisbon side and on the Ribatejo side [of the Tagus], where they set fire to many farms and caused great damage.