On 10 March 1147, King Afonso I of Portugal departed from Coimbra with 250 of his best knights intending to capture the Moorish city of Santarém, a goal that he had previously failed to achieve.
The conquest of Santarém was of vital importance to Afonso's strategy; its possession would mean the end of the frequent Moorish attacks on Leiria and would also allow a future attack on Lisbon.

The plan now was to attack the city during the night under cover of darkness, in order to catch the Moorish garrison by surprise.
King Afonso had previously sent the Portuguese Mem Ramires to Santarém disguised as a businessman, in order to secretly study the city for the conquest.

After the first day of the journey from Coimbra to Santarém, King Afonso I sent an emissary to Santarém announcing to the Moors that the truce had ended, for which three days' notice was required.
On 10 March 1147, King Afonso I of Portugal departed from Coimbra with 250 of his best knights intending to capture the Moorish city of Santarém, a goal that he had previously failed to achieve. The conquest of Santarém was of vital importance to Afonso's strategy; its possession would mean the end of the frequent Moorish attacks on Leiria and would also allow a future attack on Lisbon.
The plan now was to attack the city during the night under cover of darkness, in order to catch the Moorish garrison by surprise. King Afonso had previously sent the Portuguese Mem Ramires to Santarém disguised as a businessman, in order to secretly study the city for the conquest.
After the first day of the journey from Coimbra to Santarém, King Afonso I sent an emissary to Santarém announcing to the Moors that the truce had ended, for which three days' notice was required.
Conquest of Santarém