The Castle of Aggerhus, from its magnitude, its lofty spiral clock tower, and its elevated situation, assumes an air of grandeur, which imparts no small degree of importance to the city of Christiania. The principal, or best apartments, are in the part of the building seen beyond the clock tower. It has three fronts, one of which faces the spectator; the principal front commands the bay, and the third the city. As the chief parts of the exterior are always kept white, the castle is visible down the Fiord, and in other directions, at a vast distance. It is constructed of stone, and is situated on a grey rock, encompassed with strong and regular fortifications, the ramparts of which are well mounted with heavy cannon» The store houses contain all kinds of ammunition, &c. requisite for a siege, and for the supply of all the minor garrisons, the militia, and the surrounding country, in case of sur prise, or invasion. It is under the superintendance of a commandant, who resides there. Within the garrison walls is an area of considerable extent, laid out in spacious walks shaded by avenues of tall trees. The principal entrance is on the side next the town. There are always a considerable number of troops kept in this castle, who regularly perform garrison and town duty. The ranges of the guns around the ramparts opposite the entrance of the harbour, completely command every ship passing in and out. The walks within are much frequented as a promenade on Sundays, by the towns people and others, being on those days open to the public, like our parks, except that they are confined to pedestrians.

The castle appears to have been erected at an epoch anterior to, or coeval with the foundation of the town of Opsloe, on the opposite side of the bay, and to have been destined for its protection and defence. As that town was destroyed by a great fire, in 1624, and as at that time the side of the basin skirting its shore was probably becoming shallow, from saw-dust and other causes, which presented impediments to the shipping, it was wisely determined to build the new city on the opposite side, near the garrison, where there was deep water, and a convenient place for warehouses and wharfs. The erection of the new town appears to have been begun in the same year in which the conflagration happened, the date on the cathedral being 1624. The name of Christiania was adopted in preference to that of Opsloe or Ansloe, and the ancient harbour being entirely neglected, was gradually choaked up with saw-dust, which the oars of the ferry boats stir up, in a putrid state, every time they pass and repass from one town to the other.

Many memorable transactions have occurred respecting this garrison ; and its walls, as history testifies, have been the scene of various splendid events. There are numerous dates to be seen on different parts of it, inscribed when additions were made, or repairs completed ; as 1310, 1663, 1660, 1714, 1716. Charles XII. made the last unsuccessful attempt on it, when he and his anny were starved out, and obliged to retire without accomplishing his favourite object, the reduction of Norway.