By way of penance William and his wife founded the abbeys of St Stephen and the Holy Trinity at Caen.
The public buildings of chief interest are the kasbah, the government offices (formerly the British consulate), the palaces of the governor-general and the archbishop - all these are fine Moorish houses; the "Grand" and the "New" Mosques, the Roman Catholic cathedral of St Philippe, the church of the Holy Trinity (Church of England), and the Bibliotheque Nationale d'Alger - a Turkish palace built in 1799-1800.
The church of the Holy Trinity (built in 1870) stands at the southern end of the rue d'Isly near the site of the demolished Fort Bab Azoun.
The church of the Holy Trinity occupies the site of a Saxon monastery, which existed before 691, when the bishop of Worcester received it in exchange from Ethelred, king of Mercia.
Two years later, before the same pontiff, he preached in the city of Genoa a sermon which led to the general institution, in the countries of the obedience of Avignon, of the festival of the Holy Trinity.