The people were encamped against Gibbethon - It appears that, at this time, the Israelites had war with the Philistines, and were now besieging Gibbethon, one of their cities. This army, hearing that Zimri had rebelled and killed Elah, made Omri, their general, king, who immediately raised the siege of Gibbethon, and went to attack Zimri in the royal city of Tirzah; who, finding his affairs desperate, chose rather to consume himself in his palace than to fall into the hands of his enemies.

besieged Tirzah

Judges 9:45,50,56,57 And Abimelech fought against the city all that day; and he took the city, and slew the people that was therein, and beat down the city...

2 Kings 6:24,25 And it came to pass after this, that Benhadad king of Syria gathered all his host, and went up, and besieged Samaria...

2 Kings 18:9-12 And it came to pass in the fourth year of king Hezekiah, which was the seventh year of Hoshea son of Elah king of Israel...

2 Kings 25:1-4 And it came to pass in the ninth year of his reign, in the tenth month, in the tenth day of the month...

Luke 19:43,44 For the days shall come on you, that your enemies shall cast a trench about you, and compass you round, and keep you in on every side...

Whether a Vow Consists in a Mere Purpose of the Will?
Objection 1: It would seem that a vow consists in nothing but a purpose of the will. According to some [*William of Auxerre, Sum. Aur. III, xxviii, qu. 1; Albertus Magnus, Sent. iv, D, 38], "a vow is a conception of a good purpose after a firm deliberation of the mind, whereby a man binds himself before God to do or not to do a certain thing." But the conception of a good purpose and so forth, may consist in a mere movement of the will. Therefore a vow consists in a mere purpose of the will. Objection …
Saint Thomas Aquinas—Summa Theologica