The location of Oud Haerlem castle is on the eastern fringe of what is now Heemskerk, just west of Amsterdam.

It is 400 meter south-southeast of Assumburg Castle, which probably also dates from the thirteenth century, but was much smaller at the time.

It continued in the now disappeared Wijkermeer, and left only the dunes and a very narrow strip of land to connect the parts of Holland north and south of the IJ.

It is supposed that the counts of Holland wanted to create a defensive line on this narrow strip of land, so they could stop invasions from West Friesland further to the north.

This date was deduced from pottery from that period, which was found during works at the place of the main castle in 2000-2001.

The outer bailey of Oud Haerlem Castle was an almost rectangular structure, with one tower sticking out on the southeast corner.

Aerial photographs of the area give the impression of a Roman Legion's camp, and confirm the archaeological investigations.

In about 1248 several castles were built near Heemskerk and Beverwijk by order of count William II of Holland.

Simon then moved to Heemskerk, and gave the plot of his house in Haarlem to the Carmelites, who founded a convent on it.

Sijmon was also the first ambachtsheer of Heemskerk, which means that he had some authority that is now mostly handled by the municipality and lower judges.

[8] In 1327 Oud Haerlem Castle was sold to John I, Lord of Polanen (c. 1285-1342), with the condition that it would be an open house for the count.

John was a half brother of his father's natural son Willem van Duvenvoorde (1290-1353), financer and favorite of successive counts of Holland.

He was a favorite of Margaret II, Countess of Hainaut, and got the Huyse dat geheeten es te Hairlem with the high jurisdiction.

[11] In 1866 an enormous part of the terrain was quarried to get stones for the restoration of Brederode Castle.

In 1943 Jaap Renaud led a very short investigation on the terrain of Oud Haerlem Castle.

After Renaud's death important material surfaced, and in 2010 archaeologists Jean Roefstra and E.H.P.

What they furthermore found, was a small moat around the still existing elevation inside the terrain of the outer bailey.

[14] The conclusion of Roefstra study of Renaud's excavation, and later finds, was that the castle started out as a tower house or donjon on the elevation on the outer bailey in the mid-thirteenth century, probably built by Simon van Haerlem.

His successors filled the moat around the donjon and constructed a ring wall or enceinte, with an entrance in the square tower protruding on the southeast side.

The small square tower in the middle of the north wall provided access to the outer bailey.

The investigators tried ground-penetrating radar (GPR), magnetometry (MAG), and electromagnetic induction (EMI).

Fearing looters, Renaud never revealed the exact location, which was only recovered in a private archive after his death in 2007.

Real estate developers made all kinds of plans for the terrain in the 1990s, including the construction of a golf course.